XForms 1.0 (Third Edition)

1 About the XForms 1.0 Specification

1.1 Background

Forms are an important part of the Web, and they continue to be the primary means for enabling interactive Web applications. Web applications and electronic commerce solutions have sparked the demand for better Web forms with richer interactions. XForms 1.0 is the response to this demand, and provides a new platform-independent markup language for online interaction between a person (through an XForms Processor) and another, usually remote, agent. XForms are the successor to HTML forms, and benefit from the lessons learned from HTML forms.

Further background information on XForms can be found at http://www.w3.org/MarkUp/Forms.

1.2 Reading the Specification

This specification has been written with various types of readers in mind—in particular XForms authors and XForms implementors. We hope the specification will provide authors with the tools they need to write efficient, attractive and accessible documents without overexposing them to the XForms implementation details. Implementors, however, should find all they need to build conforming XForms Processors. The specification begins with a general presentation of XForms before specifying the technical details of the various XForms components.

The specification has been written with various modes of presentation in mind. In case of a discrepancy, the online electronic version is considered the authoritative version of the document.

This document uses the terms optional, required, recommended, may, must, and should in accord with [RFC 2119].

1.3 How the Specification is Organized

The specification is organized into the following chapters:

Chapters 1 and 2: An introduction to XForms. The introduction outlines the design principles and includes a brief tutorial on XForms.
Chapters 3 and up: XForms reference manual. The bulk of the reference manual consists of the specification of XForms. This reference defines XForms and how XForms Processors must interpret the various components in order to claim conformance.
Appendixes: Appendixes contain a normative description of XForms described in XML Schema, information on references, and other useful information.

1.4 Documentation Conventions

Throughout this document, the following namespace prefixes and corresponding namespace identifiers are used:

xforms: The XForms namespace (http://www.w3.org/2002/xforms) 3.1 The XForms Namespace
html: The XHTML namespace (http://www.w3.org/1999/xhtml) [XHTML 1.0]
xsd: The XML Schema namespace (http://www.w3.org/2001/XMLSchema)[XML Schema part 1]
xsi: The XML Schema for instances namespace (http://www.w3.org/2001/XMLSchema-instance)[XML Schema part 1]
ev: The XML Events namespace (http://www.w3.org/2001/xml-events)[XML Events]
my: Any user defined namespace

This is only a convention; any namespace prefix may be used in practice.

The following typographical conventions are used to present technical material in this document.

Official terms are defined in the following manner: [Definition: You can find most terms in chapter 13 Glossary Of Terms]. Links to terms may be specially highlighted where necessary.

The XML representations of various elements within XForms are presented using the syntax for Abstract Modules in XHTML Modularization [XHTML Modularization].

Examples are set off typographically:

Example item

Example Item

References to external documents appear as follows: [Sample Reference] with links to the references section of this document.

Sample Reference: Reference - linked to from above.

The following typesetting convention is used for non-normative commentary:

Note:

A gentle explanation or admonition to readers.

2 Introduction to XForms

XForms has been designed on the basis of several years' experience with HTML forms. HTML Forms have formed the backbone of the e-commerce revolution, and having shown their worth, have also indicated numerous ways they could be improved.

The primary difference when comparing XForms with HTML Forms, apart from XForms being in XML, is the separation of the data being collected from the markup of the controls collecting the individual values. By doing this, it not only makes XForms more tractable by making it clear what is being submitted where, it also eases reuse of forms, since the underlying essential part of a Form is no longer irretrievably bound to the page it is used in.

A second major difference is that XForms, while designed to be integrated into XHTML, is no longer restricted only to be a part of that language, but may be integrated into any suitable markup language.

XForms has striven to improve authoring, reuse, internationalization, accessibility, usability, and device independence. Here is a summary of the primary benefits of using XForms:

Strong typing: Submitted data is strongly typed and can be checked using off-the-shelf tools. This speeds up form filling since it reduces the need for round trips to the server for validation.
XML submission: This obviates the need for custom server-side logic to marshal the submitted data to the application back-end. The received XML instance document can be directly validated and processed by the application back-end.
Existing schema re-use: This obviates duplication, and ensures that updating the validation rules as a result of a change in the underlying business logic does not require re-authoring validation constraints within the XForms application.
External schema augmentation: This enables the XForms author to go beyond the basic set of constraints available from the back-end. Providing such additional constraints as part of the XForms Model enhances the overall usability of the resulting Web application.
Internationalization: Using XML 1.0 for instance data ensures that the submitted data is internationalization ready.
Enhanced accessibility: XForms separates content and presentation. User interface controls encapsulate all relevant metadata such as labels, thereby enhancing accessibility of the application when using different modalities. XForms user interface controls are generic and suited for device-independence.
Multiple device support: The high-level nature of the user interface controls, and the consequent intent-based authoring of the user interface makes it possible to re-target the user interaction to different devices.
Less use of scripting: By defining XML-based declarative event handlers that cover common use cases, the majority of XForms documents can be statically analyzed, reducing the need for imperative scripts for event handlers.

2.1 An Example

In the XForms approach, forms are comprised of a section that describes what the form does, called the XForms Model, and another section that describes how the form is to be presented.

Consider a simple electronic commerce form that might be rendered as follows:

It is clear that we are collecting a value that represents whether cash or credit card is being used, and if a credit card, its number and expiration date.

This can be represented in the XForms model element, which in XHTML would typically be contained within the head section:

<xforms:model>
  <xforms:instance>
    <ecommerce xmlns="">
      <method/>
      <number/>
      <expiry/>
    </ecommerce>
  </xforms:instance>
  <xforms:submission action="http://example.com/submit" method="post" id="submit" includenamespaceprefixes=""/>
</xforms:model>

This simply says that we are collecting three pieces of information (note that we have as yet not said anything about their types), and that they will be submitted using the URL in the action attribute.

XForms 1.0 defines a device-neutral, platform-independent set of form controls suitable for general-purpose use. The controls are bound to the XForms Model via the XForms binding mechanism, in this simple case using the ref attribute on the controls. In XHTML, this markup would typically appear within the body section (note that we have intentionally defaulted the XForms namespace prefix here):

<select1 ref="method">
  <label>Select Payment Method:</label>
  <item>
    <label>Cash</label>
    <value>cash</value>
  </item>
  <item>
    <label>Credit</label>
    <value>cc</value>
  </item>
</select1>
<input ref="number">
  <label>Credit Card Number:</label>
</input>
<input ref="expiry">
  <label>Expiration Date:</label>
</input>
<submit submission="submit">
  <label>Submit</label>
</submit>

Notice the following features of this design:

The user interface is not hard-coded to use radio buttons. Different devices (such as voice browsers) can render the concept of "select one" as appropriate.
Form controls always have labels directly associated with them as child elements—this is a key feature designed to enhance accessibility.
There is no need for an enclosing form element, as in HTML. (See 2.4 Multiple Forms per Document for details on how to author multiple forms per document)
Markup for specifying form controls has been simplified in comparison with HTML forms.

The fact that you can bind form controls to the model like this simplifies integrating XForms into other host languages, since any form control markup may be used to bind to the model.

2.2 Providing XML Instance Data

The XForms Processor can directly submit the data collected as XML. In the example, the submitted data would look like this:

Submitted Data

<ecommerce>
  <method>cc</method>
  <number>1235467789012345</number>
  <expiry>2001-08</expiry>
</ecommerce>

XForms processing keeps track of the state of the partially filled form through this instance data. Initial values for the instance data may be provided or left empty as in the example. Element instance essentially holds a skeleton XML document that gets updated as the user fills out the form. It gives the author full control on the structure of the submitted XML data, including namespace information. When the form is submitted, the instance data is serialized as an XML document. Here is an alternative version of the earlier example:

Model

<xforms:model>
  <xforms:instance>
    <payment method="cc" xmlns="http://commerce.example.com/payment">
      <number/>
      <expiry/>
    </payment>
  </xforms:instance>
  <xforms:submission action="http://example.com/submit" method="post" includenamespaceprefixes="#default"/>
</xforms:model>

In this case the submitted data would look like this:

Submitted Data

<payment method="cc" xmlns="http://commerce.example.com/payment">
  <number>1235467789012345</number>
  <expiry>2001-08</expiry>
</payment>

This design has features worth calling out:

There is complete flexibility in the structure of the XML instance data, including the use of attributes. Notice that XML namespaces are used, and that a wrapper element of the author's choosing contains the instance data.
Empty elements number and expiry serve as place-holders in the XML structure, and will be filled in with form data provided by the user.
An initial value ("cc") for the form control is provided through the instance data, in this case an attribute method. In the submitted XML, this initial value will be replaced by the user input, if the user changes the form control displaying that data.

To connect this instance data with form controls, the ref attributes on the form controls need to be changed to point to the proper part of the instance data, using binding expressions:

Binding Form Controls to Instance Nodes with ref

... xmlns:my="http://commerce.example.com/payment"
  ...
  <xforms:select1 ref="@method">...</xforms:select1>
  ...
  <xforms:input ref="my:number">...</xforms:input>
  ...
  <xforms:input ref="/my:payment/my:expiry">...</xforms:input>

Binding expressions are based on XPath [XPath 1.0], including the use of the @ character to refer to attributes, as seen here. Note that for illustrative purposes, the first two expressions make use of the XPath context node, which defaults to the top-level element (here my:payment). The third expression shows an absolute path.

2.3 Constraining Values

XForms allows data to be checked for validity as the form is being filled. In the absence of specific information about the types of values being collected, all values are returned as strings, but it is possible to assign types to values in the instance data. In this example, number should accept digits only, and should have between 14 and 18 digits and expiry should accept only valid month/date combinations.

Furthermore, the credit card information form controls for number and expiry are only relevant if the "cc" option is chosen for method, but are required in that case.

By specifying an additional component, model item properties, authors can include rich declarative validation information in forms. Such information can be taken from XML Schemas as well as XForms-specific additions, such as relevant. Such properties appear on bind elements, while Schema constraints are expressed in an XML Schema fragment, either inline or external. For example:

Declarative Validation with Model Item Properties

... xmlns:my="http://commerce.example.com/payment"...
        
  <xforms:model>
    ...
    <xforms:bind nodeset="/my:payment/my:number"
		 relevant="/my:payment/@method = 'cc'"
		 required="true()"
		 type="my:ccnumber"/>

    <xforms:bind nodeset="/my:payment/my:expiry"
		 relevant="/my:payment/@method = 'cc'"
		 required="true()"
		 type="xsd:gYearMonth"/>

    <xsd:schema ...>
      ...
      <xsd:simpleType name="ccnumber">
	<xsd:restriction base="xsd:string">
	  <xsd:pattern value="\d{14,18}"/>
	</xsd:restriction>
      </xsd:simpleType>
      ...
    </xsd:schema>
  </xforms:model>

Note:

In the above example, the relevant expression uses absolute XPath notation (beginning with /) because the evaluation context nodes for computed expressions are determined by the bind ref binding expression (see 7.4 Evaluation Context), and so any relative node path in the first bind relevant above would be relative to /my:payment/my:number

2.4 Multiple Forms per Document

XForms processing places no limits on the number of individual forms that can be placed in a single containing document. When a single document contains multiple forms, each form needs a separate model element, each with an id attribute so that they can be referenced from elsewhere in the containing document.

In addition, form controls should specify which model element contains the instance data to which they bind. This is accomplished through a model attribute that is part of the binding attributes. If no model attribute is specified on the binding element, the nearest ancestor binding element's model attribute is used, and failing that, the first XForms Model in document order is used. This technique is called 'scoped resolution', and is used frequently in XForms.

The next example adds an opinion poll to our electronic commerce form.

Adding a poll model

<xforms:model>
  <xforms:instance>
    ...payment instance data...
  </xforms:instance>
  <xforms:submission action="http://example.com/submit" method="post"/>
</xforms:model>
        
<xforms:model id="poll">
  <xforms:instance>
    <helpful/>
  </xforms:instance>
  <xforms:submission id="pollsubmit" .../>
</xforms:model>

Additionally, the following markup would appear in the body section of the document:

Form Controls for poll model

<xforms:select1 ref="/helpful" model="poll">
  <xforms:label>How useful is this page to you?</xforms:label>
  <xforms:item>
    <xforms:label>Not at all helpful</xforms:label>
    <xforms:value>0</xforms:value>
  </xforms:item>
  <xforms:item>
    <xforms:label>Barely helpful</xforms:label>
    <xforms:value>1</xforms:value>
  </xforms:item>
  <xforms:item>
    <xforms:label>Somewhat helpful</xforms:label>
    <xforms:value>2</xforms:value>
  </xforms:item>
  <xforms:item>
    <xforms:label>Very helpful</xforms:label>
    <xforms:value>3</xforms:value>
  </xforms:item>
</xforms:select1>
        
<xforms:submit submission="pollsubmit">
  <xforms:label>Submit</xforms:label>
</xforms:submit>

The main difference here is the use of model="poll", which identifies the instance. Note that submit refers to the submission element by ID and does not require binding attributes.

More XForms examples can be found in G Complete XForms Examples.

3 Document Structure

XForms 1.0 is an application of XML [XML 1.0] and has been designed for use within other XML vocabularies—in particular within a future version of XHTML [XHTML 1.0]. XForms always requires such a host language. This chapter discusses the structure of XForms that allow XForms to be used with other document types.

3.1 The XForms Namespace

The XForms namespace has the URI: http://www.w3.org/2002/xforms.

XForms Processors must use the XML namespaces mechanism [XML Names] to recognize elements and attributes from this namespace.

3.2 XForms Core Attribute Collections

3.2.1 Common Attributes

The Common Attribute Collection applies to every element in the XForms namespace.

id: The optional id attribute of type xsd:ID assigns an identity to the containing element.
anyAttribute: Foreign attributes are allowed on all XForms elements.

3.2.2 Linking Attributes

The Linking Attributes Collection applies to XForms elements which include a link to a remote resource.

src: The src attribute assigns a URI to be automatically retrieved.

Note:

Since linking attribute URIs are defined in terms of the XML Schema datatype xsd:anyURI, the same internationalization benefits and white space cautions apply as discussed in [XML Schema part 2].

Behavior of relative URIs in links is determined by the host language, although [XML Base] processing is strongly recommended.

Note:

The Forms Working Group is tracking with the HTML Working Group on a method of describing link structures.

3.2.3 Single-Node Binding Attributes

The following attributes define a binding between an XForms element such as a form control or an action and an instance data node defined by an XPath expression.

ref: Binding expression interpreted as XPath. This attribute has no meaning when a bind attribute is present.
model: Optional XForms Model selector. Specifies the ID of an XForms Model to be associated with this binding element. This attribute has no meaning for the current binding element when a bind attribute is present. Rules for determining the context XForms Model are located at 7.4 Evaluation Context.
bind: Reference to a bind element.

In this specification, when an XForms element is declared to have a Single-Node Binding, then the Single-Node Binding is required unless the element explicitly states that it is optional.

When the Single-Node Binding is required, one of ref or bind is required. When bind is used, the node is determined by the referenced bind. See 4.7.2 References to Elements within a bind Element for details on selecting an identified bind that is iterated by one or more containing bind elements.

It is an exception (4.5.1 The xforms-binding-exception Event) if the XForms Processor encounters a model IDREF value that refers to an ID not on a model element, or a bind IDREF value that refers to an ID not on a bind element.

First-node rule: When a Single-Node Binding attribute selects a node-set of size > 1, the first node in the node-set, based on document order, is used.

3.2.4 Node-Set Binding Attributes

The following attributes define a binding between an XForms element such as a form control or an action and a node-set defined by the XPath expression.

nodeset: Binding expression interpreted as XPath. This attribute has no meaning when a bind attribute is present.
model: Optional XForms Model selector. Specifies the ID of an XForms Model to be associated with this binding element. This attribute has no meaning for the current binding element when a bind attribute is present. Rules for determining the context XForms Model are located at 7.4 Evaluation Context.
bind: Reference to a bind element.

In this specification, when an XForms element is declared to have a Node-Set Binding, then the Node-Set Binding is required unless the element explicitly states that it is optional.

When the Node-Set Binding is required, one of nodeset or bind is required. When bind is used, the node-set is determined by the referenced bind. See 4.7.2 References to Elements within a bind Element for details on selecting an identified bind that is iterated by one or more containing bind elements.

It is an exception (4.5.1 The xforms-binding-exception Event) if the XForms Processor encounters a model IDREF value that refers to an id not on a model element, or a bind IDREF value that refers to an id not on a bind element.

3.2.5 Model Item Property Attributes

This collection contains one attribute for each model item property, with an attribute name exactly matching the name of the model item property, as defined in 6.1 Model Item Property Definitions.

3.3 The XForms Core Module

The XForms Core Module defines the major structural elements of XForms, intended for inclusion in a containing document. The elements and attributes included in this module are:

Element	Attributes	Minimal Content Model
model	Common, Events, functions (QNameList), schema (list of xsd:anyURI), version xforms:versionList	(instance\|xsd:schema\| submission\|bind\|Action)*
instance	Common, Linking	(ANY)
submission	Common, ref (binding-expression), bind (xsd:IDREF), action (xsd:anyURI), method ("post"\|"get"\|"put"\|"form-data-post"\|"urlencoded-post"\|qname-but-not-ncname), version (xsd:NMTOKEN), indent (xsd:boolean), mediatype (xsd:string), encoding (xsd:string), omit-xml-declaration (xsd:boolean), standalone (xsd:boolean), cdata-section-elements (QNameList), replace ("all"\|"instance"\|"none"\|QNameButNotNCNAME), instance (xsd:IDREF), separator (';' \| '&'), includenamespaceprefixes (xsd:NMTOKENS)	Action*
bind	Common, Model Item Properties, nodeset (model-binding-expression)	(bind)*

Elements defined in the XForms Actions module, when that module is included, are also allowed in the content model of model and submission, as shown above.

Within the containing document, these structural elements are typically not rendered.

The XForms Processor must ignore any foreign-namespaced attributes that are unrecognized, and must process unrecognized foreign-namespaced elements according to the 3.4 The XForms MustUnderstand Module rules.

Note that the presence of foreign namespaced elements is subject to the definition of the containing document profile.

3.3.1 The model Element

This element represents a form definition and is used as a container for elements that define the XForms Model. No restriction is placed on how many model elements may exist within a containing document.

Common Attributes: Common, Events

Attributes from XML Events are allowed on this element to facilitate creating observers. This element is not an XForms Action, and has no predefined behavior event-based behavior.

Special Attributes:

functions

Optional space-separated list of XPath extension functions (represented by QNames) required by this XForms Model. Guidance on the use of this attribute is at 7.12 Extension Functions.

schema

Optional list of xsd:anyURI links to XML Schema documents outside this model element. The XForms Processor must process all Schemas listed in this attribute. Within each XForms Model, there is a limit of one Schema per namespace declaration, including inline and linked Schemas.

Note:

The schema list may include URI fragments referring to elements located elsewhere in the containing document; e.g. "#myschema".

version

Optional attribute with a default value of empty string and legal values defined by the datatype xforms:versionList. Examples are "1.0" and "1.0 1.1". If one or more versions are indicated by this attribute on the default model, then an XForms Processor must support at least one of the listed language versions of XForms. Otherwise, the XForms Processor must terminate processing after dispatching the event xforms-version-exception to the default model. If the XForms Processor supports more than one language version indicated by the version setting on the default model or if the version setting on the default model is empty string (whether specified or by default), then the XForms Processor may execute the XForms content using any language conformance level available to it. If any non-default model has a version setting that is incompatible with the language version selected by the XForms Processor, or if any model contains an illegal version attribute value, then the XForms Processor must terminate processing after dispatching the event xforms-version-exception to the default model.

The version attribute is optional to implement, but future versions of XForms are expected to support it, so implementation support is strongly encouraged.

This example shows a simple usage of model, with the XForms namespace defaulted:

Model

<model id="Person" schema="MySchema.xsd">
  <instance src="http://example.com/cgi-bin/get-instance" />
  ...
</model>

3.3.2 The instance Element

This optional element contains or references initial instance data.

Common Attributes: Common

Special Attributes:

Linking Attributes: Optional link to externally defined initial instance data. If the link traversal fails, it is treated as an exception (4.5.2 The xforms-link-exception Event).

If both an attribute and inline content are provided, the linked version takes precedence as described at 4.2.1 The xforms-model-construct Event.

If the initial instance data is given by a link, then the instance data is formed by creating an XPath data model of the linked resource.

If the initial instance data is given by inline content, then instance data is obtained by first creating a detached copy of the inline content (including namespaces inherited from the enveloping ancestors), then creating an XPath data model over the detached copy. The detached copy must consist of content that would be well-formed XML if it existed in a separate document. Note that this restricts the element content of instance to a single child element.

If creation of the detached copy of the inline instance data fails due to an XML error, then processing should halt with an xforms-link-exception. This could happen, for example, if the inline content had two element nodes, which would imply creating an XML document with two document elements.

Note:

In XForms 1.1, a new exception event will be issued.

Note:

All data relevant to the XPath data model must be preserved during processing and submission, including processing instructions, comment nodes and all whitespace.

Note:

XForms authors who need additional control over the serialization of namespace nodes can use the includenamespaceprefixes attribute on the submission element.

3.3.3 The submission Element

This element represents declarative instructions on what to submit, and how. Details of submit processing are described at 11 Submit.

Common Attributes: Common

Special Attributes:

bind: Optional reference to a bind element. When present, the binding reference on this attribute is used in preference to any binding reference from the ref attribute.
ref: Optional selector binding expression enabling submission of a portion of the instance data. The selected node, and all descendants, are selected for submission. The default value is "/".
action: Optional attribute indicating the destination URI for submitting instance data. Behavior of relative URIs in links is determined by the host language, although [XML Base] processing is strongly recommended.
method: Required attribute specifying the protocol to be used to transmit the serialized instance data. There is no default value.
version: Optional attribute specifying the version of XML to be serialized.
indent: Optional attribute specifying whether the serializer should add extra white space nodes for readability.
mediatype: Optional attribute specifying the mediatype for XML instance serialization. Authors should ensure that the type specified is compatible with application/xml.
encoding: Optional attribute specifying an encoding for serialization.
omit-xml-declaration: Optional attribute specifying whether to omit the XML declaration on the serialized instance data.
standalone: Optional attribute specifying whether to include a standalone declaration in the serialized XML.
cdata-section-elements: Optional attribute specifying element names to be serialized with CDATA sections.
replace: Optional attribute specifying how the information returned after submit should be applied. In the absence of this attribute, "all" is assumed.
instance: Optional attribute specifying the instance to replace when the replace attribute value is "instance". When the attribute is absent, then the default is the instance that contains the submission data. An xforms-binding-exception (4.5.1 The xforms-binding-exception Event) occurs if this attribute does not indicate an instance in the same model as the submission.
separator: Optional attribute specifying the separator character between name/value pairs in urlencoding. The default value is ';'.
includenamespaceprefixes: Optional attribute providing control over namespace serialization. If absent, all namespace nodes present in the instance data are considered for serialization. If present, specifies list of namespace prefixes to consider for serialization, in addition to those visibly utilized. As in [Exc-C14N], the special value #default specifies the default namespace.

The following examples show how various options on element submission can affect serialization as application/xml. Given the following XForms fragment:

<xforms:model xmlns:xforms="http://www.w3.org/2002/xforms"
              xmlns:my="http://ns.example.org/2003">
  <xforms:instance>
    <qname xmlns="">my:sample</qname>
  </xforms:instance>
  <xforms:submission method="post" action="..."/>
</xforms:model>

Note that the includenamespaceprefixes attribute is not present, which causes all namespace nodes to be serialized, resulting in the following serialized instance data:

<qname xmlns:xforms="http://www.w3.org/2002/xforms"
       xmlns:my="http://ns.example.org/2003">my:sample</qname>

In particular, note that the XForms namespace has been serialized. To prevent this example from including the unneeded XForms namespace while maintaining the needed my prefix, includenamespaceprefixes="my" must be added to the submission element. When this attribute is present, the author takes responsibility to list all namespace prefixes not visibly utilized by the submitted instance data.

The following attributes correspond (in spelling, processing, and default values) to attributes on the output element of [XSLT 1.0], with the exception of using xsd:boolean to replace "yes"|"no":

version
indent
encoding
omit-xml-declaration
cdata-section-elements

Note:

The following XSLT attributes have no counterpart in XForms:

doctype-system
doctype-public

Elements defined in the XForms Actions module, when that module is included, are also allowed in the content model of submission.

3.3.4 The bind Element

Element bind selects a node-set selected from the instance data with a model binding expression in the nodeset attribute. Other attributes on element bind encode model item properties to be applied to each node in the node-set. When bind has an attribute of type xsd:ID, the bind then associates that identifier with the selected node-set.

Common Attributes: Common, Model Item Properties (Optional)

Special Attributes:

nodeset: An optional attribute containing a model binding expression that selects the set of nodes on which this bind operates.

See 7.4 Evaluation Context for details on how the evaluation context is determined for each attribute of the bind element..

3.4 The XForms MustUnderstand Module

Certain elements, such as extension or foreign namespaced elements defined in a host language might be critical to the operation of a particular form. To indicate this, the MustUnderstand module defines a single attribute that can be used on any element.

Element	Attributes	Minimal Content Model
ANY	xforms:mustUnderstand (xsd:boolean)	n/a

It is a terminating error that must be reported to the user if an element is marked mustUnderstand="true", and the XForms Processor does not have an implementation available for processing the element.

3.5 The XForms Extension Module

There are many different ways a host language might include XForms. One approach uses only well-formed processing, disregarding validation. Another case uses strict validation, for example XHTML 1.0, in which only predefined elements are allowed. Another common approach is to allow unregulated content in a few selected places. A host language that chooses this option can use the Extension module.

Element	Attributes	Minimal Content Model
extension	Common	ANY

3.5.1 The extension Element

Optional element extension is a container for application-specific extension elements from any namespace other than the XForms namespace. This specification does not define the processing of this element.

Common Attributes: Common

For example, RDF metadata could be attached to an individual form control as follows:

<input ref="dataset/user/email" id="email-input">
  <label>Enter your email address</label>
  <extension>
    <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
      <rdf:Description rdf:about="#email-input">
        <my:addressBook>personal</my:addressBook>
      </rdf:Description>
    </rdf:RDF>
  </extension>
</input>

4 Processing Model

This chapter defines the XForms Processing Model declaratively by enumerating the various states attained by an XForms Processor and the possible state transitions that exist in each of these states. The chapter enumerates the pre-conditions and post-conditions that must be satisfied in each of these states. XForms Processors may be implemented in any manner, so long as the end results are identical to that described in this chapter.

State transitions are in general initiated by sending events to parts of the XForms tree. The XForms Processing Model consists of events in the following categories:

Initialization
Interaction
Notification
Error Conditions

4.1 Events Overview

XForms processing is defined in terms of events, event handlers, and event responses. XForms uses the events system defined in [DOM2 Events][XML Events], with an event capture phase, arrival of the event at its Target, and finally the event bubbling phase.

Throughout this chapter, each reference to "form control" as a target element is a shorthand for any of the following elements: input, secret, textarea, output, upload, trigger, range, submit, select, select1, or group.

Event name	Cancelable?	Bubbles?	Target element
4.2 Initialization Events
xforms-model-construct	No	Yes	`model`
xforms-model-construct-done	No	Yes	`model`
xforms-ready	No	Yes	`model`
xforms-model-destruct	No	Yes	`model`
4.3 Interaction Events
xforms-previous	Yes	No	form control
xforms-next	Yes	No	form control
xforms-focus	Yes	No	form control
xforms-help	Yes	Yes	form control
xforms-hint	Yes	Yes	form control
xforms-rebuild	Yes	Yes	`model`
xforms-refresh	Yes	Yes	`model`
xforms-revalidate	Yes	Yes	`model`
xforms-recalculate	Yes	Yes	`model`
xforms-reset	Yes	Yes	`model`
xforms-submit	Yes	Yes	`submission`
4.4 Notification Events
DOMActivate	Yes	Yes	form control
xforms-value-changed	No	Yes	form control
xforms-select	No	Yes	`item` or `case`
xforms-deselect	No	Yes	`item` or `case`
xforms-scroll-first	No	Yes	`repeat`
xforms-scroll-last	No	Yes	`repeat`
xforms-insert	No	Yes	`instance`
xforms-delete	No	Yes	`instance`
xforms-valid	No	Yes	form control
xforms-invalid	No	Yes	form control
DOMFocusIn	No	Yes	form control
DOMFocusOut	No	Yes	form control
xforms-readonly	No	Yes	form control
xforms-readwrite	No	Yes	form control
xforms-required	No	Yes	form control
xforms-optional	No	Yes	form control
xforms-enabled	No	Yes	form control
xforms-disabled	No	Yes	form control
xforms-in-range	No	Yes	form control
xforms-out-of-range	No	Yes	form control
xforms-submit-done	No	Yes	`submission`
xforms-submit-error	No	Yes	`submission`
4.5 Error Indications
xforms-binding-exception	No	Yes	any element that can contain a binding expression
xforms-link-exception	No	Yes	`model`
xforms-link-error	No	Yes	`model`
xforms-compute-exception	No	Yes	`model`
xforms-version-exception	No	Yes	the default `model`

4.2 Initialization Events

This section defines the various stages of the initialization phase. The processor begins initialization by dispatching an event xforms-model-construct to each XForms Model in the containing document. How the XForms Processor itself is requested to initialize is implementation dependent.

4.2.1 The xforms-model-construct Event

Dispatched to each XForms model by the XForms processor.

Target: model

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event results in the following:

All XML Schemas are loaded. If an error occurs while attempting to access or process a remote document, processing halts with an exception (4.5.2 The xforms-link-exception Event).
If an external source for the initial instance data is given, an XPath data model [7 XPath Expressions in XForms] is constructed from it; otherwise if inline initial instance data is given, that is used instead. If the external initial instance data is not well-formed XML or cannot be retrieved, processing halts with an exception (4.5.2 The xforms-link-exception Event). If neither are given, then default processing of this event ends because the data model is not constructed in this phase, but during user interface construction (4.2.2 The xforms-model-construct-done Event).
If applicable, P3P initialized. [P3P 1.0]
Perform the behaviors of xforms-rebuild, xforms-recalculate, and xforms-revalidate in sequence on this model element without dispatching events to invoke the behaviors. The notification event markings for these operations are discarded, and the xforms-refresh behavior is not performed since the user interface has not yet been initialized.

After all XForms Models have been initialized, an xforms-model-construct-done event is dispatched to each model element.

4.2.2 The xforms-model-construct-done Event

Dispatched after the completion of xforms-model-construct processing.

Target: model

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event happens once, no matter how many XForms Models are present in the containing document, and results in the following, for each form control:

Processing can proceed in one of two different ways depending on whether an instance in a model exists when the first form control is processed.

If the instance referenced on the form control existed when the first form control was processed:

The binding expression is evaluated to ensure that it points to a node that exists. If this is not the case then the form control should behave in the same manner as if it had bound to a model item with the relevant model item property resolved to false.

If the instance referenced on the form control did not exist when the first form control for the same instance was processed:

For the first reference to an instance a default instance is created by following the rules described below.
1. A root instanceData element is created.
2. An instance data element node will be created using the binding expression from the user interface control as the name. If the name is not a valid QName, processing halts with an exception (4.5.1 The xforms-binding-exception Event).
For the second and subsequent references to an instance which was automatically created the following processing is performed:
1. If a matching instance data node is found, the user interface control will be connected to that element.
2. If a matching instance data node is not found, an instance data node will be created using the binding expression from the user interface control as the name. If the name is not a valid QName, processing halts with an exception (4.5.1 The xforms-binding-exception Event).

The above steps comprise the default processing of xforms-model-construct-done.

After all form controls have been initialized and all xforms-model-construct-done events have been processed, an xforms-ready event is dispatched to each model element.

4.2.3 The xforms-ready Event

Dispatched as part of xforms-model-construct-done processing.

Target: model

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event results in the following: None; notification event only.

4.2.4 The xforms-model-destruct Event

Bubbles: Yes

Cancelable: Yes

Context Info: None

The default action for these events results in the following: If the form control has help/hint elements supplied, these are used to construct a message that is displayed to the user. Otherwise, user agents may provide default help or hint messages, but are not required to.

4.3.4 The xforms-refresh Event

Dispatched in response to: a request to update all form controls associated with a particular XForms Model.

Target: model

Bubbles: Yes

Cancelable: Yes

Context Info: None

The default action for this event results in the following:

All UI bindings should be reevaluated as necessary.
A node can be changed by confirmed user input to a form control, by xforms-recalculate (section 4.3.6) or by the setvalue (section 10.1.9) action. If the value of an instance data node was changed, then the node must be marked for dispatching the xforms-value-changed event.
If the xforms-value-changed event is marked for dispatching, then all of the appropriate model item property notification events must also be marked for dispatching (xforms-optional or xforms-required, xforms-readwrite or xforms-readonly, and xforms-enabled or xforms-disabled).
For each form control, each notification event that is marked for dispatching on the bound node must be dispatched (xforms-value-changed, xforms-valid, xforms-invalid, xforms-optional, xforms-required, xforms-readwrite, xforms-readonly, and xforms-enabled, xforms-disabled). The notification events xforms-out-of-range or xforms-in-range must also be dispatched as appropriate. This specification does not specify an ordering for the events.
The user interface reflects the state of the model, which means that all forms controls reflect for their corresponding bound instance data:
- its current value
- its validity
- whether it is required, readonly or relevant.

4.3.5 The xforms-revalidate Event

Dispatched in response to: a request to revalidate a particular XForms Model.

Target: model

Bubbles: Yes

Cancelable: Yes

Context Info: None

An instance node is valid if and only if the following conditions hold:

the constraint model item property is true
the node satisfies all applicable XML schema definitions (including those associated by the type model item property , by an external or an inline schema, or by xsi:type)

Note:

A node that satifies the above conditions is valid even if it is required but empty.

The default action for this event results in the following:

All instance data nodes in all instance elements in the model are checked for validity according to the above definition. If the validity of a node changes, then either the xforms-valid event must be marked for dispatch if the node changes from invalid to valid or the xforms-invalid event must be marked for dispatch if the node changes from valid to invalid. Marking one of these events for dispatch unmarks the other.

4.3.6 The xforms-recalculate Event

Dispatched in response to: a request to recalculate all calculations associated with a particular XForms Model.

Target: model

Bubbles: Yes

Cancelable: Yes

Context Info: None

The default action for this event results in the following:

The values of all instance data items match their associated 'calculate' constraints, if any. All model item properties that can contain computed expressions are resolved. In addition to contributing further node value changes that will cause xforms-value-changed notifications in xforms-refresh, the model item properties that change are marked to help xforms-refresh to determine the notification events to dispatch.

If the required model item property changes, then either the xforms-required event must be marked for dispatch if required is true or the xforms-optional event must be marked for dispatch if required is false. Marking one of these events for dispatch unmarks the other.
If the readonly model item property changes, then either the xforms-readonly event must be marked for dispatch if readonly is true or the xforms-readwrite event must be marked for dispatch if readonly is false. Marking one of these events for dispatch unmarks the other.
If the relevant model item property changes, then either the xforms-enabled event must be marked for dispatch if relevant is true or the xforms-disabled event must be marked for dispatch if relevant is false. Marking one of these events for dispatch unmarks the other.

An XPath expression is bound either to the value or to a model item property (e.g., required, relevant) of one or more instance nodes. The combination of an XPath expression with a single instance node's value or model item property is considered as a single computational unit, a compute, for the purposes of recalculation.

When it is time to recalculate a model item property, the XPath expression is evaluated. The evaluation context is determined from the model binding expression that applied the model item property, as defined for computed expressions in 7.4 Evaluation Context. The XPath expression may reference or refer to another instance node, in which case the value of the instance node is referenced. Each referenced instance node has as dependents those computes which directly refer to the instance node. References to the current node's value in calculate expressions are explicitly ignored, i.e., if an expression associated with a compute refers to the instance node associated with the compute, then the instance node does not take itself as a dependent. A compute is computationally dependent on an instance node (whose value may or may not be computed) if there is a path of dependents leading from the instance node through zero or more other instance nodes to the compute. A compute is part of a circular dependency if it is computationally dependent on itself.

Note:

Authors should not refer to the current node's value in calculate expressions because the effect is not well-defined. Other model item properties, such as required or readonly, however, are well-defined in the presence of self-references.

When a recalculation event begins, there will be a list L of one or more instance nodes whose values may have been changed, e.g., by user input being propagated to the instance.

An XForms Processor must recalculate computes for nodes in L and nodes that are computationally dependent on nodes in L.
An XForms Processor must perform only a single recalculation of each compute that is computationally dependent on one or more of the elements in L.
An XForms Processor must recalculate a compute C after recalculating all computes of instance nodes on which C is computationally dependent. (Equivalently, an XForms Processor must recalculate a compute C before recalculating any compute that is computationally dependent on the instance node associated with C.)
Finally, if a compute is part of a circular dependency and also computationally dependent on an element in L, then an XForms processor must report an exception (4.5.4 The xforms-compute-exception Event).

D Recalculation Sequence Algorithm describes one possible method for achieving the desired recalculation behavior.

4.3.7 The xforms-rebuild Event

Dispatched in response to: a request to rebuild the internal data structures that track computational dependencies within a particular XForms Model.

Target: model

Bubbles: Yes

Cancelable: Yes

Context Info: None

The default action for this event results in the following:

All model item properties are initialized by processing all bind elements in document order. For each bind:

If the attribute nodeset is attached to the bind, it is evaluated to select an XPath node-set. Otherwise, if the bind does not have a nodeset attribute, then the selected XPath node-set consists of the in-scope evaluation context.
For each node in the selected XPath node-set, model item properties are applied according to the remaining attributes on the bind element (for details on the model item properties, see 6 Model Item Properties). If a node already contains a model item property of the same name due to the processing of prior bind elements, then XForms processing for the containing document halts with an exception (4.5.1 The xforms-binding-exception Event).
For each node in the selected XPath node-set, any child bind elements are recursively processed as described in the three points of this list.

After initial processing of the bind elements, the computational dependency data structures are rebuilt, and then the change list L is set to contain references to all instance nodes that have an associated computational expression so that a full recalculation is performed the next time the behavior of xforms-recalculate is invoked.

4.3.8 The xforms-reset Event

Dispatched in response to: a user request to reset the model.

Target: model

Bubbles: Yes

Cancelable: Yes

Context Info: None

The default action for this event results in the following:

The instance data is reset to the tree structure and values it had immediately after having processed the xforms-ready event. Then, the events xforms-rebuild, xforms-recalculate, xforms-revalidate and xforms-refresh are dispatched to the model element in sequence.

4.3.9 The xforms-submit Event

See chapter 11 Submit.

4.4 Notification Events

4.4.1 The DOMActivate Event

Dispatched in response to: the "default action request" for a form control, for instance pressing a button or hitting enter.

Target: form control

Bubbles: Yes

Cancelable: Yes

Context Info: None

The default action for this event results in the following: None; notification event only.

4.4.2 The xforms-value-changed Event

Dispatched in response to: a change to an instance data node bound to a form control.

Target: form control

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event results in the following: None; notification event only.

This event is dispatched during 4.3.4 The xforms-refresh Event if the bound instance data node has been marked for dispatching this event due to a change.

Note:

For incremental processing, this specification does not define how often XForms Processors fire these events. Implementations are expected to optimize processing (for instance not flashing the entire screen for each character entered, etc.).

Note:

The change to the instance data associated with this event happens before the event is dispatched.

4.4.3 The xforms-select and xforms-deselect Events

Dispatched in response to: an item in a select, select1, or switch becoming selected or deselected.

Target: item or case

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event results in the following: None; notification event only.

4.4.4 The xforms-scroll-first and xforms-scroll-last Events

Dispatched in response to: a setindex action attempting to set an index outside the range of a repeat.

Target: repeat

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event results in the following: None; notification event only.

Dispatched in response to: a form control receiving focus.

Target: form control

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event results in the following: None; notification event only.

4.4.9 The DOMFocusOut Event

Dispatched in response to: a form control losing focus.

Target: form control

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event results in the following: None; notification event only.

4.4.10 The xforms-readonly Event

Dispatched in response to: an instance data node either changing and being or becoming readonly.

Dispatched in response to: completion of submit processing, including processing any returned document.

Target: submission

Bubbles: Yes

Cancelable: No

Context Info: None

The default action for this event results in the following: None; notification event only.

4.4.19 The xforms-submit-error Event

Dispatched as an indication of: a failure of the submit process, as defined at 11 Submit

Target: submission

The previous sections describe processing associated with individual events. This section gives the overall sequence of related events that must occur in several common situations. In the following lists, events that may be fired more than once are prefixed with [n].

4.6.1 For `input`, `secret`, `textarea`, `range`, or `upload` Controls

When the form control is interactively changed, and has the "incremental="true" setting, the event sequence described at 4.6.7 Sequence: Value Change may be initiated at implementation dependent intervals.
When the form control is interactively changed and does not have the "incremental=true" setting, no events are required to be dispatched, and thus no order is defined.
When focus changes from the form control and the value has changed, the event sequence is as described at 4.6.7 Sequence: Value Change.

4.6.2 For `output` Controls

No event sequences are defined.

4.6.3 For `select` or `select1` Controls

When a selection is interactively changed, and the form control has the "incremental="true" setting, the event sequence is described at 4.6.6 Sequence: Selection Without Value Change, which may be followed immediately by the sequence described at 4.6.7 Sequence: Value Change.
When a selection is interactively changed, and the form control does not have the "incremental="true" setting, the event sequence is described at 4.6.6 Sequence: Selection Without Value Change.
When focus changes from the form control and the value has changed, the event sequence is as described at 4.6.7 Sequence: Value Change.

4.6.4 For `trigger` Controls

Activating the form control causes the event sequence defined at 4.6.8 Sequence: Activating a Trigger.

4.6.5 For `submit` Controls

Activating the form control causes the event sequence defined at 4.6.8 Sequence: Activating a Trigger, followed immediately by the event sequence defined at 4.6.9 Sequence: Submission.

4.6.6 Sequence: Selection Without Value Change

xforms-deselect
xforms-select

4.6.7 Sequence: Value Change

xforms-recalculate
xforms-revalidate
xforms-refresh performs reevaluation of UI binding expressions then dispatches these events according to value changes, model item property changes and validity changes:
- [n] xforms-value-changed
- [n] xforms-valid or xforms-invalid
- [n] xforms-enabled or xforms-disabled
- [n] xforms-optional or xforms-required
- [n] xforms-readonly or xforms-readwrite
- [n] xforms-out-of-range or xforms-in-range
(The order in which these events are dispatched is not defined).
Perform further deferred updates as necessary

4.6.8 Sequence: Activating a Trigger

DOMActivate

4.6.9 Sequence: Submission

xforms-submit
xforms-submit-done or xforms-submit-error

4.7 Resolving ID References in XForms

The element of a document for which an IDREF must be resolved is called the source element, and the element bearing the matching ID, if there is one, is called the target element. Due to the run-time expansion of repeated content in XForms, it is possible that there will be more than one occurrence of both the source and target elements. This section describes how XForms IDREF resolution works to accommodate such repetition of the originating document's content.

Each run-time occurrence of the source element is called a source object, and each run-time occurrence of the target element is called a target object. It is the source object that performs the IDREF resolution, and the result of the search is either null or a target object.

Whether or not repeated content is involved, a null search result for an IDREF resolution is handled differently depending on the source object. If there is a null search result for the target object and the source object is an XForms action such as dispatch, send, setfocus, setindex or toggle, then the action is terminated with no effect. Similarly, a submit form control does not dispatch xforms-submit if its submission attribute does not indicate an existing submission element. Likewise, when an XPath function associated with the source object performs the IDREF search and a null result is obtained, the function returns an empty result such as NaN for the index() function or empty nodeset for the instance() function. However, an xforms-binding-exception occurs if there is a null search result for the target object indicated by attributes bind, model and instance.

If the target element is not repeated, then the search for the target object is trivial since there is only one associated with the target element that bears the matching ID. This is true regardless of whether or not the source object is repeated. However, if the target element is repeated, then additional information must be used to help select a target object from among those associated with the identified target element.

4.7.1 References to Elements within a repeat Element

When the target element that is identified by the IDREF of a source object has one or more repeat elements as ancestors, then the set of ancestor repeats are partitioned into two subsets, those in common with the source element and those that are not in common. Any ancestor repeat elements of the target element not in common with the source element are descendants of the repeat elements that the source and target element have in common, if any.

For the repeat elements that are in common, the desired target object exists in the same set of run-time objects that contains the source object. Then, for each ancestor repeat of the target element that is not in common with the source element, the current index of the repeat determines the set of run-time objects that contains the desired target object.

4.7.2 References to Elements within a bind Element

When a source object expresses a Single Node Binding or Node Set Binding with a bind attribute, the IDREF of the bind attribute is resolved to a target bind object whose associated nodeset is used by the Single Node Binding or Node Set Binding. However, if the target bind element has one or more bind element ancestors, then the identified bind may be a target element that is associated with more than one target bind object.

If a target bind element is outermost, or if all of its ancestor bind elements have nodeset attributes that select only one node, then the target bind only has one associated bind object, so this is the desired target bind object whose nodeset is used in the Single Node Binding or Node Set Binding. Otherwise, the in-scope evaluation context node of the source object containing the bind attribute is used to help select the appropriate target bind object from among those associated with the target bind element.

From among the bind objects associated with the target bind element, if there exists a bind object created with the same in-scope evaluation context node as the source object, then that bind object is the desired target bind object. Otherwise, the IDREF resolution produced a null search result.

5 Datatypes

This chapter defines the datatypes used in defining an XForms Model.

5.1 XML Schema Built-in Datatypes

XForms supports all XML Schema datatypes except for xsd:duration, xsd:ENTITY, xsd:ENTITIES, and xsd:NOTATION. Concepts value space, lexical space and constraining facets are as specified in [XML Schema part 2]. Certain XML Schema datatypes have been identified as part of a smaller XForms conformance profile that is being developed separately, and are marked with an asterisk *. XForms includes datatypes derived by restriction and derived by list from these base types. XForms Processors must treat the datatypes listed in the chapter as in-scope without requiring the inclusion of an XML Schema.

Built-in primitive types:

xsd:dateTime *
xsd:time *
xsd:date *
xsd:gYearMonth *
xsd:gYear *
xsd:gMonthDay *
xsd:gDay *
xsd:gMonth *
xsd:string *
xsd:boolean *
xsd:base64Binary *
xsd:hexBinary
xsd:float
xsd:decimal *
xsd:double
xsd:anyURI *
xsd:QName

Note:

The built-in datatype xsd:duration is not supported, except as an abstract datatype. Instead, either xforms:dayTimeDuration or xforms:yearMonthDuration should be used.

Built-in derived types:

xsd:normalizedString
xsd:token
xsd:language
xsd:Name
xsd:NCName
xsd:ID
xsd:IDREF
xsd:IDREFS
xsd:NMTOKEN
xsd:NMTOKENS
xsd:integer *
xsd:nonPositiveInteger *
xsd:negativeInteger *
xsd:long *
xsd:int *
xsd:short *
xsd:byte *
xsd:nonNegativeInteger *
xsd:unsignedLong *
xsd:unsignedInt *
xsd:unsignedShort *
xsd:unsignedByte *
xsd:positiveInteger *

5.2 XForms Datatypes

The Schema for XForms derives the following types to facilitate defining model in XForms.

5.2.1 xforms:listItem

This datatype serves as a base for the xforms:listItems datatype. The value space for listItem permits one or more characters valid for xsd:string, except white space characters.

5.2.2 xforms:listItems

XForms includes form controls that produce simpleType list content. This is facilitated by defining a derived-by-list datatype. The value space for listItems is defined by list-derivation from listItem.

Note:

In most cases, it is better to use markup to distinguish items in a list. See 9.3.3 The itemset Element.

5.2.3 xforms:dayTimeDuration

XForms includes a totally ordered duration datatype that can represent a duration of days, hours, minutes, and fractional seconds. The value space for this datatype is the set of fractional second values. This datatype is derived from xsd:duration.

5.2.4 xforms:yearMonthDuration

XForms includes a totally ordered duration datatype that can represent a duration of a whole number of months and years. The value space for this datatype is the set of integer month values. This datatype is derived from xsd:duration.

6 Model Item Properties

This chapter defines infoset contributions that can be bound to instance data nodes with element bind (see 3.3.4 The bind Element). The combination of these contributions to an instance data node is called a model item. Taken together, these contributions are called model item properties, and are defined in the following section. In contrast, the term Schema constraint refers only to XML Schema constraints from the facets of a given datatype.

6.1 Model Item Property Definitions

Model item properties can be distinguished along various axes.

Computed expressions vs. fixed properties:

Fixed properties are static values that the XForms Processor evaluates only once. Such properties consist of literals, and are not subject to XPath evaluation.
Computed expressions are XPath expressions that provide a value to the XForms Processor. Such values are recalculated at certain times as specified by the XForms Processing Model (see 4 Processing Model). These expressions encode dynamic properties, often constraints, such as the dependency among various data items. Computed expressions are not restricted to examining the value of the instance data node to which they apply. XPath expressions provide the means to traverse the instance data; more complex computations may be encoded as call-outs to external scripts.

Inheritance rules:

Some model item properties define inheritance rules, in which case the XForms Processor needs to keep track of two separate values: 1) the local value, which is applied from an attribute of element bind, and 2) the inherited value, which is determined by combining the evaluated local value with the evaluated values from ancestor nodes in the instance data.

Note:

The sample recalculation algorithm defined in D Recalculation Sequence Algorithm is defined to operate only on the local values of a model item property. It assumes that an implementation propagates the combined values to a node's descendants.

Assigning local values:

Local values are assigned by processing all bind elements in an XForms Model in document order. It is an error to attempt to set a model item property twice on the same node. The details of this process are given at 4.2.1 The xforms-model-construct Event.

The following sections list the model item properties available as part of all model items. For each, the following information is provided:

Description
Computed Expression (yes or no)
Legal Values
Default Value
Inheritance Rules

6.1.1 The type Property

Description: The type model item property can be applied to both elements and attributes. The type model item property is not applied to instance nodes that contain child elements. The type model item property associates a datatype (as defined in [XML Schema part 2]) with the string-value (as defined in [XPath 1.0]) of an instance node. The datatype being associated can be obtained from a simpleType definition or a simpleContent definition from a complexType. If the datatype cannot be obtained as just described, then the Default Value of xsd:string is used.

Computed Expression: No.

Legal Values: Any xsd:QName representing a datatype definition in an XML Schema. The namespace context from the parent bind of the type attribute is used to resolve the namespace qualification of the value.

Default Value: xsd:string.

Inheritance Rules: does not inherit.

Associating datatypes with instance nodes

<model xmlns:my="http://example.org">  

   <xsd:schema targetNamespace="http://example.org" xmlns:my="http://example.org">
      <xsd:simpleType name="Currency">
	<xsd:restriction base="xsd:string">
           <xsd:enumeration value="USD"/>
           <xsd:enumeration value="EUR"/>
	</xsd:restriction>
      </xsd:simpleType>
      
      <xsd:complexType name="Price">
         <xsd:simpleContent>
            <xsd:extension base="xsd:double">
               <xsd:attribute name="currency" type="my:Currency" use="optional" default="USD"/>
            </xsd:extension>
         </xsd:simpleContent>
      </xsd:complexType>
   </xsd:schema>        
        
   <instance>
      <data xmlns="http://example.org">
         <aString>Hello, world!</aString>
         <simpleType>
            <price>100.00</price>
            <price>abc</price>
            <price currency="EUR">100.00</price>
            <price currency="EUR">abc</price>
         </simpleType>
         <complexType>
            <price>100.00</price>
            <price>abc</price>
            <price currency="abc">100.00</price>
            <price currency="EUR">abc</price>
         </complexType>
      </data>
   </instance>

   <bind nodeset="my:aString" type="xsd:string"/>
   <bind nodeset="my:simpleType/my:price" type="xsd:double"/>
   <bind nodeset="my:complexType/my:price" type="my:Price"/>
   <bind nodeset="my:complexType/my:price[3]/@currency" type="my:Currency"/>
   <bind nodeset="/my:data" type="xsd:string"/>
   
</model>

The first bind expresses the default datatype of xsd:string.

The second and third binds place type model item properties on each of the four price element children of the elements simpleType and complexType. Both binds associate the datatype xsd:double with the nodes. In both cases, the first and third nodes are considered valid according to the type model item property because their content matches the xsd:double datatype constraint. For both binds, the second and fourth price nodes are not valid due to their content.

The fourth bind places a type model item property on the currency attribute of the third price element. According to this association, the currency attribute node is not valid because its content does not match the enumeration given for my:Currency. Note that the containing element price is valid according to its type model item property.

The fifth bind attempts to associate a datatype with the data element. The association is ignored since the data element contains child elements.

6.1.2 The readonly Property

Description: describes whether the value is restricted from changing.

Computed Expression: Yes.

Legal Values: Any expression that is convertible to XPath boolean with boolean().

Default Value: false(), unless a calculate property is specified, then true().

Inheritance Rules: If any ancestor node evaluates to true, this value is treated as true. Otherwise, the local value is used.

Note:

This is the equivalent of taking the logical OR of the evaluated readonly property on the local and every ancestor node.

When evaluating to true, this model item property indicates that the XForms Processor should not allow any changes to the bound instance data node.

In addition to restricting value changes, the readonly model item property provides a hint to the XForms user interface. Form controls bound to instance data with the readonly model item property should indicate that entering or changing the value is not allowed. This specification does not define any effect on visibility, focus, or navigation order.

Attaching a readonly property

<instance>
  <my:person-name>
    <my:first-name>Roland</my:first-name>
    <my:last-name/>
  </my:person-name>
</instance>
<bind nodeset="/my:person-name/my:first-name" readonly="true()"/>

Here, we have associated a readonly property with an element.

6.1.3 The required Property

Description: describes whether a value is required before the instance data is submitted.

Computed Expression: Yes.

Legal Values: Any expression that is convertible to XPath boolean with boolean().

Default Value: false().

Inheritance Rules: does not inherit.

A form may require certain values, and this requirement may be dynamic. When evaluating to true, this model item property indicates that a non-empty instance data node is required before a submission of instance data can occur. Non-empty is defined as:

If the bound instance data node is an element, the element must not have the xsi:nil attribute set to true.
The value of the bound instance data node must be convertible to an XPath string with a length greater than zero.

Except as noted below, the required model item property does not provide a hint to the XForms user interface regarding visibility, focus, or navigation order. XForms authors are strongly encouraged to make sure that form controls that accept required data are visible. An XForms Processor may provide an indication that a form control is required, and may provide immediate feedback, including limiting navigation. Chapter 4 Processing Model contains details on how the XForms Processor enforces required values.

Attaching a required property

<instance>
  <my:person-name>
    <my:first-name>Roland</my:first-name>
    <my:last-name />
  </my:person-name>
</instance>
<bind nodeset="/my:person-name/my:last-name" required="true()"/>

Here, we have associated a required property with element my:last-name to indicate that a value must be supplied.

Note:

XML Schema has a similarly named concept with use="required|optional|prohibited". This is different than the XForms Model item property, in two ways: 1) use applies only to attributes, while XForms required applies to any node. 2) use is concerned with whether the entire attribute must be specified (without regard to value), while required determines whether a value is required of the node before submission.

6.1.4 The relevant Property

Description: indicates whether the model item is currently relevant. Instance data nodes with this property evaluating to false are not serialized for submission.

Computed Expression: Yes.

Legal Values: Any expression that is convertible to XPath boolean with boolean().

Default Value: true().

Inheritance Rules: If any ancestor node evaluates to XPath false, this value is treated as false. Otherwise, the local value is used.

Note:

This is the equivalent of taking the logical AND of the evaluated relevant property on the local and every ancestor node.

Many forms have data entry sections that depend on other conditions. For example, a form might ask whether the respondent owns a car. It is only appropriate to ask for further information about their car if they have indicated that they own one.

The relevant model item property provides information to the XForms user interface regarding visibility, focus, and navigation order. In general, when true, associated form controls should be made visible. When false, associated form controls (and any children) and group and switch elements (including content) must be made unavailable, removed from the navigation order, and not allowed focus. Typically, non-relevant content is not presented, or it may be styled as disabled.

Note:

A form control, group or switch must express a single node binding in order to be associated with an instance node.

Attaching a relevant property

<instance>
  <my:order>
    <my:item>
      <my:amount />
      <my:discount>100</my:discount>
    </my:item>
  </my:order>
</instance>
<bind nodeset="my:item/my:discount" readonly="true()"
      relevant="../my:amount &gt; 1000"/>

Here, we have associated a relevant property with element my:discount to indicate a discount is relevant when the order amount is greater than 1000.

6.1.5 The calculate Property

Description: supplies an expression used to calculate a string value for the associated instance data node.

Computed Expression: Yes.

Legal Values: Any XPath expression.

Default Value: none.

Inheritance Rules: does not inherit.

An XForms Model may include model items whose string values are computed from other values. For example, the sum over line items for quantity times unit price, or the amount of tax to be paid on an order. Such computed values can be expressed with calculate properties, whose XPath expressions are evaluated and converted to strings with the XPath string() function. Chapter 4 Processing Model contains details of when and how the calculation is performed.

Attaching a calculate property

<instance>
  <my:order>
    <my:item>
      <my:amount />
      <my:discount />
    </my:item>
  </my:order>
</instance>
<bind nodeset="my:item/my:discount" calculate="../my:amount * 0.1"
      relevant="../my:amount &gt; 1000"/>

Here, we have associated a relevant property with element my:discount to indicate a discount of 10% is relevant when the order amount is greater than 1000.

6.1.6 The constraint Property

Description: specifies a predicate that needs to be satisfied for the associated instance data node to be considered valid.

Computed Expression: Yes.

Legal Values: Any expression that is convertible to XPath boolean with boolean().

Default Value: true().

Inheritance Rules: does not inherit.

When evaluating to XPath false, the associated model item is not valid; the converse is not necessarily true. Chapter 4 Processing Model contains details of when and how the constraint is calculated as well as when validation is performed.

Attaching a constraint property

<instance>
  <my:range>
    <my:from />
    <my:to />
  </my:range>
</instance>
<bind nodeset="my:to" constraint=". &gt; ../my:from" />

Here, a constraint property associated with element my:to indicates that its value must be greater than that of element my:from.

Note:

Specifying minimum and maximum occurrences for nodes in the instance data can be achieved by using the count() function within a constraint property.

6.1.7 The p3ptype Property

Description: Attaches a P3P data element to an instance data node, indicating the specific kind of data collected there.

Computed Expression: No.

Legal Values: xsd:string.

Default Value: none

Inheritance Rules: does not inherit.

This model item property holds a description of the kind of data collected by the associated instance data node, based on the P3P datatype system [P3P 1.0]. This information may be used to enhance the form-fill experience, for example by supplying previously-known data.

Attaching a type constraint using Binding

<instance>
  <my:person-name>
    <my:first-name />
    <my:last-name />
  </my:person-name>
</instance>
<bind type="my:nonEmptyString" nodeset="my:first-name"
      p3ptype="user.name.given"/>

Here, we have attached both XML Schema and P3P type information to element first-name via element bind.

6.2 Schema Constraints

Chapter 5 Datatypes described how XForms uses the XML Schema datatype system to constrain the value space of data values collected by an XForms Model. Such datatype constraints can be provided via an XML Schema. Alternatively, this section lists various mechanisms for attaching type constraints to instance data. Attributes xsi:schemaLocation and xsi:noNamespaceSchemaLocation are ignored for purposes for locating a Schema.

6.2.1 Atomic Datatype

The XForms Processing Model applies XML Schema facets as part of the validation process. At the simplest level, it is necessary to associate a set of facets (through an XML Schema datatype) with a model item. This has the effect of restricting the allowable values of the associated instance data node to valid representations of the lexical space of the datatype.

The set of facets associated with a model item must be determined by the following list, as if it were processed in the given order. When multiple datatype restrictions apply to the same model item, the combination of all given restrictions must apply. Note that it is possible to produce a combination of restrictions that is impossible to satisfy; authors are encouraged to avoid this practice.

An XML Schema associated with the instance data.
An XML Schema xsi:type attribute in the instance data.
An XForms type constraint associated with the instance data node using XForms binding.
If no type constraint is provided, the instance data node defaults to type="xsd:string" (default to string rule).

The following declares a datatype based on xsd:string with an additional constraining facet.

Type Constraint Using XML Schema

<xsd:simpleType name="nonEmptyString">
  <xsd:restriction base="xsd:string">
    <xsd:minLength value="1"/>
  </xsd:restriction>
</xsd:simpleType>

This new datatype would then be associated with one or more model items through one of the methods outlined here.

Attaching A Type Constraint

<my:first-name xsi:type="my:nonEmptyString"/>

This defines element first-name to be of type my:nonEmptyString.

Attaching Type Constraint Using XForms Binding

<instance>
  <my:first-name />
</instance>
<bind type="my:nonEmptyString" nodeset="/my:first-name"/>

Here, we have attached type information to element first-name via element bind. Thus the XForms author can extend external schemas without having the ability to change them.

7 XPath Expressions in XForms

XForms uses XPath to address instance data nodes in binding expressions, to express constraints, and to specify calculations. XPath expressions that are not syntactically valid, including attempted calls to undefined functions, result in an exception (4.5.4 The xforms-compute-exception Event), except for binding expressions, which produce a different exception (4.5.1 The xforms-binding-exception Event).

7.1 XPath Datatypes

XPath datatypes are used only in binding expressions and computed expressions. XForms uses XPath datatypes boolean, string, number, and node-set. A future version of XForms is expected to use XPath 2.0, which includes support for XML Schema datatypes.

7.2 Feature string for the hasFeature method call

For this version of the XForms specification, the feature string for the [DOM2 Core] DOMImplementation interface hasFeature method call is "org.w3c.xforms.dom" and the version string is "1.0".

7.3 Instance Data

For each model element, the XForms Processor maintains the state in an internal structure called instance data that conforms to the XPath Data Model [XPath 1.0]. XForms Processors that implement DOM must provide DOM access to this instance data via the interface defined below.

Note:

Instance data always has a single root element, and thus corresponds to a DOM Document.

The IDL for this interface follows:

#include "dom.idl"

pragma prefix "w3c.org"

module xforms {
  interface XFormsModelElement : dom::Element {
    dom::Document getInstanceDocument(in dom::DOMString instanceID)
      raises(dom::DOMException);
    void rebuild();
    void recalculate();
    void revalidate();
    void refresh();
  };
};

7.3.1 The getInstanceDocument() Method

If the instance-id parameter is the empty string, then the document element of the default instance is returned. Otherwise, this method returns a DOM Document that corresponds to the instance data associated with the instance element containing an ID matching the instance-id parameter. If there is no matching instance data, a DOMException is thrown.

7.3.2 The rebuild() Method

This method signals the XForms Processor to rebuild any internal data structures used to track computational dependencies within this XForms Model. This method takes no parameters and raises no exceptions.

7.3.3 The recalculate() Method

This method signals the XForms Processor to perform a full recalculation of this XForms Model. This method takes no parameters and raises no exceptions.

7.3.4 The revalidate() Method

This method signals the XForms Processor to perform a full revalidation of this XForms Model. This method takes no parameters and raises no exceptions.

7.3.5 The refresh() Method

This method signals the XForms Processor to perform a full refresh of form controls bound to instance nodes within this XForms Model. This method takes no parameters and raises no exceptions.

7.4 Evaluation Context

Within XForms, the default model is the first model in document order. The default instance of any model is the first child instance in document order within that model.. XPath expressions appearing in various XForms attributes are used to reference instance data . Every XPath expression requires an evaluation context consisting of a node, position, size, variable bindings, function set, and namespace context. For all evaluation contexts in XForms,

No variable bindings are in place.
The available function library is defined below in 7.6 The XForms Function Library.
Any namespace declarations in scope for the attribute that defines the expression are applied to the expression.
The context node, position and size are determined according to rules described below.

A binding element is any element that is explicitly allowed to have a binding expression attribute, and a bound element is any element that explicitly declares a binding expression attribute. A binding expression attribute contains an XPath expression that references zero or more nodes of instance data. Every XPath expression requires an evaluation context. The in-scope evaluation context of a binding element provides an evaluation context for the binding expression attribute. The following rules are used in determining the node, position and size of the in-scope evaluation context:

A binding element is "outermost" if the element has no ancestor binding elements. If an outermost binding element is contained by a model, then the context node for the outermost binding element is the top-level document element node of the default instance of the containing model element. Otherwise, the context node for outermost binding elements is the top-level document element node of the default instance in the default model. For outermost binding elements, the context size and position are 1.
The context node, position and size for non-outermost binding elements is determined using the binding expression attribute or in-scope evaluation context of the nearest ancestor binding element. This is also referred to as "scoped resolution". For a non-outermost binding element:
1. If the nearest ancestor binding element is not a bound element, then the in-scope evaluation context of the non-outermost binding element is equivalent to the in-scope evaluation context of the nearest ancestor binding element.
2. If the nearest ancestor binding element expresses a Single-Node binding, then the in-scope evaluation context of the non-outermost binding element has a context size and position of 1 and the context node is the one resulting from the Single-Node binding of the nearest ancestor binding element.
3. If the nearest ancestor binding element expresses a Node Set binding, then the XForms processor dynamically generates an occurrence of the non-outermost binding element for each of the nodes in the Node Set Binding of the nearest ancestor binding element. The dynamic in-scope evaluation context for each generated occurrence of the non-outermost binding element has a context size equal to the size of the nodeset identified by the Node Set Binding of the nearest ancestor binding element, the context node is the node for which the occurrence of the non-outermost binding element was generated, and the position is equal to the position of the generator node in the nodeset identified by the Node Set Binding of the nearest ancestor binding element.
4. If the nearest ancestor binding element expresses a Node Set binding, then the non-outermost binding element has its own in-scope evaluation context separately from those of its dynamically generated occurences described above. The in-scope evaluation context has a context position of 1, and the context node and size are set by the first node and the size of the nodeset identified by the Node Set binding of the nearest ancestor binding element.
Once the context node of the in-scope evaluation context has been determined according to the rules above, if the binding element expresses a model attribute that refers to a model other than the one containing the context node, then the context node of the in-scope evaluation context is changed to be the top-level document element node of the default instance of the referenced model, and the context position and size are changed to 1.

Note:

The rules above for determining the in-scope evaluation context are applicable to XForms elements that can contain a binding expression attribute even if they cannot contain a Single Node Binding or Node Set Binding. The elements bind and submission are examples.

The in-scope evaluation context of an element that is not a binding element is the same as if the element were a binding element. For example, the in-scope evaluation context for the setindex action element is required to provide the context for evaluating the index attribute, so it is determined as if the element could contain a binding expression attribute.

XPath expressions also appear in model item property attributes of the bind element to define computed expressions. If the bind element does not express a Node Set binding, then the in-scope evaluation context for model item property attributes of the bind is equal to the in-scope evaluation context for the bind. Otherwise, the bind has a Node Set binding, and computed expressions for each model item property attribute are generated for each node. For each computed expression generated, the evaluation context node, position and size are determined by the same method as dynamic in-scope evaluation context rule above, except the computed expression is used in lieu of a binding expression attribute such that the bind element is the nearest ancestor binding element.

XPath expressions also appear in the special attributes of several other XForms elements, such as the value attribute on setvalue and output, the at attribute of insert and delete, or the index attribute of setindex. Generally, if the containing element does not express a Single Node Binding or Node Set Binding, then the special attribute is evaluated using the in-scope evaluation context. Special attributes may be evaluated using the in-scope evaluation context even if the containing element expresses a Single Node Binding or Node Set Binding. However, for some special attributes, the evaluation context node, position and size are based on the result of the Single Node Binding or Node set Binding. Each special attribute that contains an XPath expression describes how its evaluation context node, position and size are determined.

In the following example, the group has a binding expression of level2/level3. According to the rules above, this outermost element node would have a context node of /level1, which is the document element node of the instance data. The select1 form control then inherits a context node from the parent group.

Sample XML Instance Data

<level1>
  <level2>
    <level3 attr="xyz"/>
  </level2>
</level1>

Binding Expression Context Nodes

<group ref="level2/level3">
  <select1 ref="@attr" ... >
     <label>...</label>
  </select1>
</group>

This section describes how the in-scope evaluation context of an element is determined, not whether the in-scope evaluation will be used. The Single-Node Binding or Node Set Binding of a non-outermost binding element is not evaluated if the in-scope evaluation context does not contain a context node. This can occur if the Single-Node Binding or Node Set Binding of the nearest ancestor bound element produces an empty nodeset. Also, if the Single-Node Binding or Node Set Binding of an element is expressed with the bind attribute, then the resulting node or nodeset is obtained from the referenced bind element. The nodeset attribute of a bind element is evaluated using the in-scope evaluation of the bind element, not the in-scope evaluation context of an element that references it with a bind attribute.

7.5 Binding Expressions

A binding expression is an XPath expression used in binding a model item property to one or more instance nodes, or to bind a form control to instance data, or to specify the node or node set for operation by an action. By default, all binding expressions refer to the first instance within the context model. This behavior can be changed with the instance() function.

7.5.1 Dynamic Dependencies

Not every possible XPath expression is acceptable as a binding expression. In particular, there are restrictions on model binding expressions that create dynamic dependencies, which are defined as follows:

An XPath predicate (in square brackets) is a possibly implicit boolean test. A dynamic dependency exists on any predicate unless all terms in the test are "fixed", where fixed means either a constant, or a value that will not change between operations explicitly defined as rebuilding computational dependencies.

Note:

For purposes of determining dynamic dependencies, the following subexpressions are considered fixed: position(), last(), count(), and property(). This is because the specification mandates a dependency rebuild after any event that could change the values returned by these functions.

Another dynamic dependency is any use of the id() function, unless both the parameter to the function and the matching attribute of type xsd:ID are fixed. In the same way, the instance() function is dynamic unless the parameter to the function is fixed.

XPath variables that change in value from one recalculate to the next would also create dynamic dependencies (though XForms 1.0 defines an empty variable context for all XPath expressions).

Authors that define extension functions are encouraged to follow these rules.

7.5.2 Model Binding Expressions

A model binding expression is a kind of binding expression that can be used to declare model item properties, and is used in attributes of the bind element.

Dynamic dependencies in model binding expressions will generally require manual rebuilding of dependencies.

7.5.3 UI Binding Expressions

Binding references can be used to bind form controls to the underlying instance data as described here. Different attribute names, ref and nodeset distinguish between a single node and a node-set respectively. See 3.2.3 Single-Node Binding Attributes and 3.2.4 Node-Set Binding Attributes.

Dynamic dependences are allowed in UI binding expressions based on the conformance profile.

7.5.4 UI Binding in other XML vocabularies

The XForms binding mechanism allows other XML vocabularies to bind user interface controls to an XForms Model using any of the techniques shown here. As an example, XForms binding attribute bind might be used within XHTML 1.x user interface controls as shown below. See 3.2.3 Single-Node Binding Attributes and 3.2.4 Node-Set Binding Attributes.

XForms Binding In XHTML 1.x User Interface Controls

<html:input type="text" name="..." xforms:bind="fn"/>

7.5.5 Binding Examples

Consider the following document with the one-and-only XForms model:

<xforms:model id="orders">
  <xforms:instance xmlns="">
    <orderForm>
      <shipTo>
        <firstName>John</firstName>
      </shipTo>
    </orderForm>
  </xforms:instance>
  <xforms:bind nodeset="/orderForm/shipTo/firstName" id="fn" />
</xforms:model>

The following examples show three ways of binding user interface control xforms:input to instance element firstName declared in the model shown above.

UI Binding Using Attribute ref

<xforms:input ref="/orderForm/shipTo/firstName">...

UI Binding Using Attribute bind

<xforms:input bind="fn">...

Specifies Model Containing The Instance Explicitly

<xforms:input model="orders" ref="/orderForm/shipTo/firstName">...

7.6 The XForms Function Library

The XForms Function Library includes the entire [XPath 1.0] Core Function Library, including operations on node-sets, strings, numbers, and booleans.

The following sections define additional required functions for use within XForms : 7.7 Boolean Functions, 7.8 Number Functions, 7.9 String Functions, 7.10 Date and Time Functions and 7.11 Node-set Functions.

The function library provided by an XForms processor may also contain other extension functions as described in 7.12 Extension Functions.

7.7 Boolean Functions

7.7.1 The boolean-from-string() Function

boolean boolean-from-string(string)

Function boolean-from-string returns true if the required parameter string is "true" or "1", or false if parameter string is "false", or "0". This is useful when referencing a Schema xsd:boolean datatype in an XPath expression. If the parameter string matches none of the above strings, according to a case-insensitive comparison, the return value is false.

7.7.2 The if() Function

string if(boolean, string, string)

Function if evaluates the first parameter as boolean, returning the second parameter when true, otherwise the third parameter.

7.8 Number Functions

7.8.1 The avg() Function

number avg(node-set)

Function avg returns the arithmetic average of the result of converting the string-values of each node in the argument node-set to a number. The sum is computed with sum(), and divided with div by the value computed with count(). If the parameter is an empty node-set, or if any of the nodes evaluate to NaN, the return value is NaN.

7.8.2 The min() Function

number min(node-set)

Function min returns the minimum value of the result of converting the string-values of each node in argument node-set to a number. "Minimum" is determined with the < operator. If the parameter is an empty node-set, or if any of the nodes evaluate to NaN, the return value is NaN.

7.8.3 The max() Function

number max(node-set)

Function max returns the maximum value of the result of converting the string-values of each node in argument node-set to a number. "Maximum" is determined with the < operator. If the parameter is an empty node-set, or if any of the nodes evaluate to NaN, the return value is NaN.

7.8.4 The count-non-empty() Function

number count-non-empty(node-set)

Function count-non-empty returns the number of non-empty nodes in argument node-set. A node is considered non-empty if it is convertible into a string with a greater-than zero length.

7.8.5 The index() Function

number index(string)

Function index takes a string argument that is the IDREF of a repeat and returns the current 1-based position of the repeat index for the identified repeat—see 9.3.1 The repeat Element for details on repeat and its associated repeat index. if the specified argument does not identify a repeat, the function returns NaN.

Note:

The IDREF obtained from the function parameter may not uniquely identify the desired repeat if the repeat element bearing the matching ID resides in a repeating construct such as element repeat. The general method described in 4.7 Resolving ID References in XForms is used to determine the desired run-time repeat object.

index

<xforms:trigger>
  <xforms:label>Add to Shopping Cart</xforms:label>
  <xforms:insert ev:event="DOMActivate" position="after"
                 nodeset="items/item" at="index('cartUI')"/>
</xforms:trigger>

7.9 String Functions

7.9.1 `The property() Function`

string property(string)

Function property returns the XForms property named by the string parameter.

The following properties are available for reading (but not modification).

version: version is defined as the string "1.0" for XForms 1.0.
conformance-level: conformance-level strings are defined in 12 Conformance.

property

<xforms:instance>
  ...
  <xforms:bind nodeset="message"
               calculate="concat( 'created with XForms ', property('version'))"/> ...
</xforms:instance>

7.10 Date and Time Functions

Note:

The following XML Schema datatypes do not have specific functions for manipulation within XForms expressions: xsd:time, xsd:gYearMonth, xsd:gYear, xsd:gMonthDay, xsd:gDay, xsd:gMonth. Extension functions (7.12 Extension Functions) may be used to perform needed operations on these datatypes.

7.10.1 The now() Function

string now()

The now function returns the current system date and time as a string value in the canonical XML Schema xsd:dateTime format. If time zone information is available, it is included (normalized to UTC). If no time zone information is available, an implementation default is used.

Note:

Attaching a calculation of "now()" to an instance data node would not result in a stream of continuous recalculations of the XForms Model.

7.10.2 The days-from-date() Function

number days-from-date(string)

This function returns a whole number of days, according to the following rules:

If the string parameter represents a legal lexical xsd:date or xsd:dateTime, the return value is equal to the number of days difference between the specified date or dateTime (normalized to UTC) and 1970-01-01. Hour, minute, and second components are ignored after normalization. Any other input parameter causes a return value of NaN.

Examples:

days-from-date("2002-01-01") returns 11688
days-from-date("1969-12-31") returns -1

7.10.3 The seconds-from-dateTime() Function

number seconds-from-dateTime(string)

This function returns a possibly fractional number of seconds, according to the following rules:

If the string parameter represents a legal lexical xsd:dateTime, the return value is equal to the number of seconds difference between the specified dateTime (normalized to UTC) and 1970-01-01T00:00:00Z. If no time zone is specified, UTC is used. Any other input string parameter causes a return value of NaN.

7.10.4 The seconds() Function

number seconds(string)

This function returns a possibly fractional number of seconds, according to the following rules:

If the string parameter represents a legal lexical xsd:duration, the return value is equal to the number specified in the seconds component plus 60 * the number specified in the minutes component, plus 60 * 60 * the number specified in the hours component, plus 60 * 60 * 24 * the number specified in the days component. The sign of the result will match the sign of the duration. Year and month components, if present, are ignored. Any other input parameter causes a return value of NaN.

Examples:

seconds("P1Y2M") returns 0
seconds("P3DT10H30M1.5S") returns 297001.5
seconds("3") returns NaN

Note:

Even though this function is defined based on a lexical xsd:duration, it is intended for use only with derived-from-xsd:duration datatypes, specifically xforms:dayTimeDuration.

7.10.5 The months() Function

number months(string)

This function returns a whole number of months, according to the following rules:

If the string parameter represents a legal lexical xsd:duration, the return value is equal to the number specified in the months component plus 12 * the number specified in the years component. The sign of the result will match the sign of the duration. Day, hour, minute, and second components, if present, are ignored. Any other input parameter causes a return value of NaN.

Examples:

months("P1Y2M") returns 14
months("-P19M") returns -19

Note:

Even though this function is defined based on a lexical xsd:duration, it is intended for use only with derived-from-xsd:duration datatypes, specifically xforms:yearMonthDuration.

7.11 Node-set Functions

7.11.1 The instance() Function

node-set instance(string?)

An XForms Model can contain more than one instance. This function allows access to instance data, within the same XForms Model, but outside the instance data containing the context node.

If the argument is omitted or is equal to the empty string, then the root element node (also called the document element node) is returned for the default instance in the model that contains the current context node.

Otherwise, the argument is converted to a string as if by a call to the string function. This string is treated as an IDREF, which is matched against instance elements in the containing document. If a match is located, and the matching instance data is associated with the same XForms Model as the current context node, this function returns a node-set containing just the root element node (also called the document element node) of the referenced instance data. In all other cases, an empty node-set is returned.

Example:

For instance data corresponding to this XML:

<xforms:instance xmlns="" id="orderform">
  <orderForm>
    <shipTo>
      <firstName>John</firstName>
    </shipTo>
  </orderForm>
</xforms:instance>

The following expression selects the firstName node. Note that the instance function returns an element node, effectively replacing the leftmost location step from the path:

ref="instance('orderform')/shipTo/firstName"

7.12 Extension Functions

XForms documents may use additional XPath extension functions beyond those described here. A number of useful community extensions are defined at [EXSLT]. The names of any such extension functions must be declared in attribute functions on element model. Such declarations are used by the XForms Processor to check against available extension functions. XForms Processors perform this check at the time the document is loaded, and stop processing by signaling an exception (4.5.4 The xforms-compute-exception Event) if the XForms document declares an extension function for which the processor does not have an implementation.

Note:

Explicitly declaring extension functions enables XForms Processors to detect the use of unimplemented extension functions at document load-time, rather than throwing a fatal error during user interaction. Failure by authors to declare extension functions will result in an XForms Processor potentially halting processing during user interaction with a fatal error.

8 Form Controls

8.1 The XForms Form Controls Module

Form controls are declared using markup elements, and their behavior refined via markup attributes.

Element	Attributes	Minimal Content Model
input	Common, UI Common, Single Node Binding, inputmode (xsd:string), incremental (xsd:boolean)	label, (UI Common)*
secret	Common, UI Common, Single Node Binding, inputmode (xsd:string), incremental (xsd:boolean)	label, (UI Common)*
textarea	Common, UI Common, Single Node Binding, inputmode (xsd:string), incremental (xsd:boolean)	label, (UI Common)*
output	Common, Single Node Binding (optional), appearance ("full"\|"compact"\|"minimal"\|QNameButNotNCNAME), value (XPath Expression)	label?
upload	Common, UI Common, Single Node Binding, mediatype (xsd:string), incremental (xsd:boolean)	label, filename?, mediatype?, (UI Common)*
range	Common, UI Common, Single Node Binding, start (xsd:string), end (xsd:string), step (xsd:string), incremental (xsd:boolean)	label, (UI Common)*
trigger	Common, UI Common, Single Node Binding (optional)	label, (UI Common)*
submit	Common, UI Common, Single Node Binding (optional), submission (xsd:IDREF)	label, (UI Common)*
select	Common, UI Common, Single Node Binding, selection ("open" \| "closed"), incremental (xsd:boolean)	label, (List UI Common)+, (UI Common)*
select1	Common, UI Common, Single Node Binding, selection ("open" \| "closed"), incremental (xsd:boolean)	label, (List UI Common)+, (UI Common)*
choices	Common	label?, (List UI Common)+
item	Common	label, value, (UI Common)*
filename	Common, Single Node Binding	EMPTY
mediatype	Common, Single Node Binding	EMPTY
value	Common, Single Node Binding (optional)	(PCDATA\|ANY)*
label	Common, Single Node Binding (optional), Linking	(PCDATA\|(UI Inline))*
help	Common, Single Node Binding (optional), Linking	(PCDATA\|(UI Inline))*
hint	Common, Single Node Binding (optional), Linking	(PCDATA\|(UI Inline))*
alert	Common, Single Node Binding (optional), Linking	(PCDATA\|(UI Inline))*

Note:

Unless bound to form controls, instance data nodes are not presented to the user; consequently, there is no need for a form control corresponding to HTML input type="hidden".

The following attributes are common to many user-interface related XForms elements, here called the UI Common attribute group.

Element	Attributes
(various)	appearance ("full"\|"compact"\|"minimal"\|QNameButNotNCNAME)

appearance: Optional attribute to define an appearance hint. if absent, the user agent may freely choose any suitable rendering.

Note:

A host language is expected to add attributes such as xml:lang as well as an attribute, named class, that holds a list of strings that can be matched by CSS class selectors.

Further, a host language must provide a way to indicate overall navigation order among form controls and other elements included in the host language, as well as keyboard or direct access navigation to specific elements. One such proposal is to uses a pair of attributes named navindex and accesskey, defined as follows:

navindex

Optional attribute is a non-negative integer in the range of 0-32767 used to define the navigation sequence. This gives the author control over the sequence in which form controls are traversed. The default navigation order is specified in the chapter 4 Processing Model.

accesskey

Optional attribute defines a shortcut for moving the input focus directly to a particular form control. The value of this is a single character which when pressed together with a platform specific modifier key (e.g., the alt key) results in the focus being set to this form control.

The user agent must provide a means of identifying the accesskeys that can be used in a presentation. This may be accomplished in different ways by different implementations, for example through direct interaction with the application or via the user's guide. The accesskey requested by the author might not be made available by the player (for example it may not exist on the device used, or it may be used by the player itself). Therefore the user agent should make the specified key available, but may map the accesskey to a different interaction behavior.

Additionally, this module defines the following content sets:

Content Set	Minimal Content Model
UI Common	(help\|hint\|alert\|Action)*
List UI Common	(choices\|item\|itemset)+
Form Controls	(input\|secret\|textarea\|output\|upload\|range\|trigger\|submit\|select\|select1)*
UI Inline	(output)*

As shown above, the XML Events module adds the Actions content set into the UI Common content set. A host language should add inline markup to the Inline content set. When the XForms Extension module is present, it too should be included in the UI Common content set.

8.1.1 Implementation Requirements Common to All Form Controls

XForms user interface controls are bound to the underlying instance data using binding attributes as defined in the chapter 6 Model Item Properties.

Form controls enable accessibility by taking a uniform approach to such features as labels, help text, navigation, and keyboard shortcuts. Internationalization issues are addressed by following the same design principles as in XHTML. All form controls are suitable for styling as aural or visual media.

Form controls encapsulate high-level semantics without sacrificing the ability to deliver real implementations. For instance, the form control select enables the user to select items from a set. These form controls distinguish the functional aspects of the underlying control from the presentational and behavioral aspects. This separation enables the expression of the intent underlying a particular form control—see [AUI97] for a definition of such high-level user interaction primitives.

Form controls when rendered display the underlying data values to which they are bound. While the data presented to the user through a form control must directly correspond to the bound instance data, the display representation is not required to match the lexical value. For example, user agents should apply appropriate conventions to the display of dates, times, durations and numeric values including separator characters.

All form controls must meet the following implementation requirements:

If a form control violates its data binding restriction, an xforms-binding-exception must occur.
Form controls that write simpleContent to instance data must do so exactly as defined by the XForms Action 10.1.9 The setvalue Element
All form controls that read simpleContent instance data must do so as follows:
- Element nodes: If element child nodes are present, then an xforms-binding-exception occurs. Otherwise, if text child nodes are present, returns the string-value of the first text child node. Otherwise, returns "" (the empty string).
- Attribute nodes: returns the string-value of the node.
- Text nodes: returns the string-value of the node.
- Namespace, processing instruction, comment, and the XPath root node: behavior is undefined.
Form controls must distinguish rendering between valid and invalid states. Control of this behavior should be made available to stylesheets.
Form controls must indicate when the bound instance data contains a value the form control is not capable of rendering. Control of this behavior should be made available to stylesheets.
Form controls must render upon request an explanation of the current state of a form control, including validity and associated model item properties. Control of this behavior should be made available to stylesheets.
Form controls must provide a default explanation for the above when no user-specified explanation is available.
Form controls are considered to be non-relevant if any of the following apply:
- the Single Node Binding is expressed and resolves to empty nodeset,
- the Single Node Binding is expressed and resolves to a non-relevant instance node,
- the form control is contained by a non-relevant switch or group (which includes a non-relevant repeat item), or
- the form control is contained by a non-selected case element of a switch.
When a form control becomes non-relevant, it must receive event xforms-disabled and then the XForms action handlers that are listening for events on the non-relevant form control must be disabled.
When a non-relevant form control changes to being relevant, the XForms action handlers that listen for events on the form control must become enabled and then the form control must be updated to represent the current value(s) and model item properties of the instance node(s) to which it is bound or to which it refers. The following events must be dispatched to the form control: xforms-enabled, xforms-value-changed, one of xforms-valid or xforms-invalid, one of xforms-readonly or xforms-readwrite, one of xforms-required or xforms-optional, and one of xforms-in-range or xforms-out-of-range.

Sections in this chapter define the various form controls by specifying the following:

Description
Common Attributes
Special Attributes
Examples
Data Binding Restrictions
Implementation Requirements

8.1.2 The input Element

Description: This form control enables free-form data entry.

Common Attributes: Common, UI Common, Single Node Binding

Special Attributes:

inputmode: Optional. This form control accepts an input mode hint. E Input Modes.
incremental: when true, this form control will generate additional xforms-value-changed events. The default value for this attribute is false.

Example:

<input ref="order/shipTo/street" class="streetAddress">
  <label>Street</label>
  <hint>Please enter the number and street name</hint>
</input>

In the above, the class attribute can be used by a style sheet to specify the display size of the form control. Note that the constraints on how much text can be input are obtained from the underlying XForms Model definition and not from these display properties.

A graphical browser might render the above example as follows:

An average-looking text entry form control. The label, 'Street' has been aligned to the left

Data Binding Restrictions: Binds to any simpleContent (except xsd:base64Binary, xsd:hexBinary or any datatype derived from these).

Implementation Requirements: Must allow entry of a lexical value for the bound datatype. Implementations should provide a convenient means for entry of datatypes and take into account localization and internationalization issues such as representation of numbers. For example, an input bound to an instance data node of type xsd:date might provide a calendar control to enter dates; similarly, an input control bound to of type boolean might be rendered as a checkbox.

<input ref="order/shipDate">
  <label>Ship By</label>
  <hint>Please specify the ship date for this order.</hint>
</input>

A graphical browser might render the above example as follows:

A text box for a date control, with a button to open into a calendar.

The user can type a date into the text edit box, or press the button to open a calendar:

A calendar picker graphical widget.

8.1.3 The secret Element

Description: This form control is used to provide the user with the ability to supply information to the system in a manner that makes it difficult for someone, other than the user, who may be observing the process to discern the value that is being supplied. A common use is for password entry.

Common Attributes: Common, UI Common, Single Node Binding

Special Attributes:

inputmode: Optional. This form control accepts an input mode hint. E Input Modes.
incremental: when true, this form control will generate additional xforms-value-changed events. The default value for this attribute is false.

Example:

Password Entry

<secret ref="/login/password">
  <label>Password</label>
  <hint>The password you enter will not be displayed.</hint>
</secret>

A graphical browser might render this form control as follows:

A password entry form control, with '*' characters where the text would be expected and a hint box displaying hint text.

Data Binding Restrictions: Identical to input.

Implementation Requirements: Implementations, including accessibility aids, must obscure the value being entered into this form control. One possible approach would be to render a "*" or similar character instead of the actual characters entered. Note that this provides only a casual level of security; truly sensitive information will require additional security measures outside the scope of XForms.

8.1.4 The textarea Element

Description: This form control enables free-form data entry and is intended for use in entering multiline content, e.g., the body of an email message.

Common Attributes: Common, UI Common, Single Node Binding

Special Attributes:

inputmode: Optional. This form control accepts an input mode hint. E Input Modes.
incremental: when true, this form control will generate additional xforms-value-changed events. The default value for this attribute is false.

Example:

Email Message Body

<textarea ref="message/body" class="messageBody">
  <label>Message Body</label>
  <hint>Enter the text of your message here</hint>
</textarea>

A graphical browser might render the above example as follows:

A larger-than-average text entry form control. The title, 'Message Body:' provides an additional hint that large amounts of text are allowed here.

Data Binding Restrictions: Binds to xsd:string or any derived simpleContent.

Implementation Requirements: Must allow entry of a lexical value for the bound datatype, including multiple lines of text.

8.1.5 The output Element

Description: This form control renders a value from the instance data, but provides no means for entering or changing data. It is used to display values from the instance, and is treated as display:inline for purposes of layout. Element output can be used to display the value at a particular location in the instance by using a binding expression; it can also be used to display the result of evaluating an XPath expression by specifying the XPath expression to be evaluated via attribute value instead of ref. Note that attributes ref and value on element output are mutually exclusive.

Common Attributes: Common, Single Node Binding (optional)

Special Attributes:

appearance: This form control does not use the UI Common attribute group, but nevertheless still contains an optional appearance attribute, as defined above.
value: Optional. An XPath expression to be evaluated. The string result of the evaluation is rendered by the form control. If binding attributes are present to select a node, this attribute has no effect. The evaluation context is the same as would be applied to the evaluation of the single node binding. This XPath expression is re-evaluated whenever there is a change in any node to which the expression refers.

Example:

Explanatory Message

I charged you -
<output ref="order/totalPrice"/>
- and here is why:

A graphical browser might render an output form control as follows:

Average-looking text, reading 'I charged you 100.0 - and here is why:'

Data Binding Restrictions: Binds to any simpleContent.

Implementation Requirements: Must allow display of a lexical value for the bound datatype. Implementations should provide a convenient means for display of datatypes and take into account localization and internationalization issues such as representation of numbers.

8.1.6 The upload Element

Description: This form control enables the common feature found on Web sites to upload a file from the local file system, as well as accepting input from various devices including microphones, pens, and digital cameras.

Common Attributes: Common, UI Common, Single Node Binding

Special Attributes:

mediatype: Optional. Space-separated list of suggested media types, used by the XForms Processor to determine the possible sources of data to upload.
incremental: When true, this form control will generate additional xforms-value-changed events. The default for this form control is false.

Example:

Uploading An Image

<upload ref="mail/attachment" mediatype="image/*">
  <label>Select image:</label>
  <filename ref="@filename" />
  <mediatype ref="@mediatype" />
</upload>

A graphical browser might render this form control as follows:

A drop-down box; main display reads 'Select Image:' with a cute icon. The drop-down itself has three items: (icon)-From Scanner or Camera...; (icon)-Scribble...; Browse...

Implementation Requirements:

On activation, if child element filename is present and a filename is available, upload places the filename of the data to upload in the instance at the node indicated by the binding attributes on child element filename.
On activation, if child element mediatype is present and a mediatype is available, upload places the mediatype of the data to upload in the instance at the node indicated by the binding attributes on child element mediatype.

Data Binding Restrictions: This form control can only be bound to datatypes xsd:anyURI, xsd:base64Binary or xsd:hexBinary, or types derived by restriction from these.

Implementation Requirements: For base64Binary or hexBinary data binding:

When bound to an instance data node of type xsd:base64binary, xsd:hexBinary, or a type derived by restriction thereof, on activation upload places the binary content in the content of the node with the indicated encoding.

Implementation Requirements: For anyURI data binding:

When bound to an instance data node of type xsd:anyURI (or a type derived by restriction thereof), on activation upload places a URI in the content of the node.
For security reasons, the XForms Processor must not dereference the URI bound to this form control without explicit user permission.
Note:
Implementors note that upload must associate the binary content, mediatype, and filename with that URI for 11.4 Serialization as multipart/related and 11.5 Serialization as multipart/form-data serialization.

Implementations with a file system should support file upload—selecting a specific file. The types of files presented by default should reflect the mediatype specified by attribute mediatype, for example defaulting to only audio file types in the file dialog when the mediatype is "audio/*".

Implementation Requirements: For all data bindings:

Implementations with specific pen/digitizer hardware should (and implementations with other pointing devices may) support scribble—allowing in-place creation of pen-based data.
Implementations with specific audio recording capabilities should support record audio—in-place recording of an audio clip.
Implementations with a digital camera, scanner interface or screen capture should support acquire image—in-place upload of images from an attached device.
Implementations with video recording capability should provide a record video option.
Implementations with 3d capabilities should provide a 3d interface option.
Implementations may provide proprietary implementations (for example, a mediatype of text/rtf could invoke an edit window with a proprietary word processing application)
Implementations are encouraged to support other input devices not mentioned here.
Implementations which cannot support upload for the given mediatype must make this apparent to the user.

See the child elements filename 8.3.1 The filename Element and mediatype 8.3.2 The mediatype Element.

8.1.7 The range Element

Description: This form control allows selection from a sequential range of values.

Common Attributes: Common, UI Common, Single Node Binding

Special Attributes:

start: Optional hint for the lexical starting bound for the range—a legal value for the underlying data. If provided, this value is used to further refine the constraints specified by the underlying model.
end: Optional hint for the ending bound for the range—a legal value for the underlying data. If provided, this value is used to further refine the constraints specified by the underlying model.
step: Optional value to use for incrementing or decrementing the value. Must be of a type capable of expressing the difference between two legal values of the underlying data.
incremental: When true, this form control will generate additional xforms-value-changed events. The default for this form control is false.

Example:

Picking From A Range

<range ref="/stats/balance" start="-2.0" end="2.0" step="0.5">
  <label>Balance</label>
</range>

A graphical browser might render this as follows:

a slider control, from -2 to +2

Data Binding Restrictions: Binds only the following list of datatypes, or datatypes derived by restriction from those in the list: xsd:duration, xsd:date, xsd:time, xsd:dateTime, xsd:gYearMonth, xsd:gYear, xsd:gMonthDay, xsd:gDay, xsd:gMonth, xsd:float, xsd:decimal, xsd:double.

Implementation Requirements: Must allow input of a value corresponding to the bound datatype. Implementations should inform the user of the upper and lower bounds, as well as the step size, if any. If the instance data value is outside the upper or lower bounds, this form control must indicate an out-of-range condition. In graphical environments, this form control may be rendered as a "slider" or "rotary control".

Notice that the attributes of this element encapsulate sufficient metadata that in conjunction with the type information available from the XForms Model proves sufficient to produce meaningful prompts when using modalities such as speech, e.g., when using an accessibility aid. Thus, in the example below, an aural user agent might speak a prompt of the form Please pick a date in the range January 1, 2001 through December 31, 2001.

In the event of overlapping restrictions between the underlying datatype and the start and end hints, the most restrictive range should be used.

Example:

Picking a date from a range

<range ref="/order/shipDate" start="2001-01-01" end="2001-12-31">
  <label>Ship Date</label>
</range>

8.1.8 The trigger Element

Description: This form control is similar to the HTML element button and allows for user-triggered actions. This form control may also be used to construct other custom form controls.

Common Attributes: Common, UI Common, Single Node Binding (optional)

Example:

Simple Trigger

<trigger>
  <label>Click here</label>
</trigger>

Data Binding Restrictions: Binds to any node. This form control does not directly interact with form data, but is affected by model item properties of the bound node, thus binding attributes are not required.

Implementation Requirements: The user agent must provide a means to generate an DOMActivate event on the form control. Graphical implementations might render this form control as a push-button with the label on the button face. Style sheets can be used to style this form control as an image, hyperlink, or other presentation.

8.1.9 The submit Element

Description: This form control initiates submission of all or part of the instance data to which it is bound.

Common Attributes: Common, UI Common, Single Node Binding (optional)

Special Attributes:

submission: Required reference to element submission.

Example:

Submit

<submit submission="timecard">
  <label>Submit Timecard</label>
</submit>

Implementation Requirements: The default action for event DOMActivate is to dispatch event xforms-submit to the submission element specified by required attribute submission. Upon activation, this control must become unavailable for further activations until the submit process concludes with either an xforms-submit-done or xforms-submit-error event.

8.1.10 The select Element

Description: This form control allows the user to make multiple selections from a set of choices.

Common Attributes: Common, UI Common, Single Node Binding

Special Attributes:

selection: Optional attribute determining whether free entry is allowed in the list. Default is "closed".
incremental: When true, this form control will generate additional xforms-value-changed events. The default for this form control is true.

Example:

Selecting Ice Cream Flavor

<select ref="my:flavors">
  <label>Flavors</label>
  <choices>
    <item>
      <label>Vanilla</label>
      <value>v</value>
    </item>
    <item>
      <label>Strawberry</label>
      <value>s</value>
    </item>
    <item>
      <label>Chocolate</label>
      <value>c</value>
    </item>
  </choices>
</select>

In the above example, more than one flavor can be selected.

A graphical browser might render form control select as any of the following:

`appearance="full"`	`appearance="compact"`	`appearance="minimal"`

Typically, a style sheet would be used to determine the exact appearance of form controls, though a means is provided to suggest an appearance through attribute appearance. The value of the attribute consists of one of the following values:

"full": all choices should be rendered at all times.
"compact": a fixed number of choices should be rendered, with scrolling facilities as needed
"minimal": a minimum number of choices should be rendered, with a facility to temporarily render additional choices

Data Binding Restrictions: any simpleContent capable of holding a sequence. The restriction to binding simpleContent exists when the choices are authored as part of the user interface control as shown in this section. Element itemset for creating dynamic selections described in 9.3.3 The itemset Element allows the available choices to be obtained from an XForms Model, and when using that construct, the data binding restriction to simpleContent is relaxed.

Note:

A limitation of the XML Schema list datatypes is that white space characters in the storage values (the value element) are always interpreted as separators between individual data values. Therefore, authors should avoid using white space characters within storage values with list simpleContent.

Incorrect Type Declaration

<item>
  <value>United States of America</value>
  ...
</item>

When selected, this item would introduce not one but four additional selection values: "America", "of", "States", and "United".

Implementation Requirements: The label for each choice must be presented, allowing at any number of selections, possibly none. This form control stores the values corresponding to the selected choices as a space separated list in the location addressed by attribute ref. The values to be stored are either directly specified as the contents of element value, or specified indirectly through binding attributes on element value.

Note that the datatype bound to this form control may include a non-enumerated value space, e.g., xsd:string, or a union of a enumeration and a non-enumerated datatype (called an open enumeration). In this case, control select may have attribute selection="open". The form control should then allow free data entry, as described in 8.1.2 The input Element. The form control may permit multiple values to be entered through free entry.

For closed selections: If the initial instance value matches the storage value of one or more of the given items, those items are selected. If there is no match, no items are initially selected. If any selected values do not have a choice with a matching storage value, the form control must indicate an out-of-range condition.

For open selections: If the initial instance values match the storage value specified by one or more of the items, the all such matching items are selected. If the initial instance values do not match the storage value specified by one or more of the items, all such non-matching items are included as selected values, as if entered through free entry. Free entry text is handled the same as form control input 8.1.2 The input Element, possibly in multiplicity. When using dynamic selections with complexTypes, open selection has no effect.

Implementation Hints: An accessibility aid might allow the user to browse through the available choices and leverage the grouping of choices in the markup to provide enhanced navigation through long lists of choices.

8.1.11 The select1 Element

Description: This form control allows the user to make a single selection from multiple choices.

Common Attributes: Common, UI Common, Single Node Binding

Special Attributes:

selection: Optional attribute determining whether free entry is allowed in the list. Default is "closed".
incremental: When true, this form control will generate additional xforms-value-changed events. The default for this form control is true.

Example:

Pick A Flavor

<select1 ref="my:flavor">
  <label>Flavor</label>
  <item>
    <label>Vanilla</label>
    <value>v</value>
  </item>
  <item>
    <label>Strawberry</label>
    <value>s</value>
  </item>
  <item>
    <label>Chocolate</label>
    <value>c</value>
  </item>
</select1>

In the above example, selecting one of the choices will result in the associated value given by element value on the selected item being set in the underlying instance data at the location icecream/flavor.

A graphical browser might render this form control as any of the following:

appearance="full"	appearance="compact"	appearance="minimal"

Data Binding Restrictions: Binds to any simpleContent. The restriction to binding simpleContent exists when the choices are authored as part of the user interface control as shown in this section. Element itemset for creating dynamic selections described in 9.3.3 The itemset Element allows the available choices to be obtained from an XForms Model, and when using that construct, the data binding restriction to simpleContent is relaxed.

Implementation Requirements: The label for each choice must be presented, allowing at all times exactly one selection. This form control stores the value corresponding to the selected choice in the location addressed by attribute ref. The value to be stored is either directly specified as the contents of element value, or specified indirectly through binding attributes on element value.

Note that the datatype bound to this form control may include a non-enumerated value space, e.g., xsd:string, or a union of a enumeration and a non-enumerated datatype (called an open enumeration). In this case, control select1 may have attribute selection="open". The form control should then allow free data entry, as described in 8.1.2 The input Element.

For closed selections: If the initial instance value matches the storage value of one of the given items, that item is selected. If there is no match, the form control must indicate an out-of-range condition..

For open selections: If the initial instance value matches the storage value specified by one of the items, the first such matching item is selected. Otherwise, the selected value is the initial lexical value. Free entry text is handled the same as form control input 8.1.2 The input Element.

User interfaces may choose to render this form control as a pulldown list or group of radio buttons, among other options. The appearance attribute offers a hint as to which rendering might be most appropriate, although any styling information (such as CSS) should take precedence.

8.2 Common Markup for Selection Controls

8.2.1 The choices Element

This element is used within selection form controls to group available choices. This provides the same functionality as element optgroup in HTML.

Common Attributes: Common

8.2.2 The item Element

This element specifies the storage value and label to represent an item in a list. It is found within elements select1 and select, or grouped in element choices.

Common Attributes: Common

8.2.3 The value Element

This element provides a storage value to be used when an item is selected.

Common Attributes: Common, Single Node Binding (optional)

Data Binding Restriction: All lexical values must be valid according to the datatype bound to the selection control.

If inline content and a Single Node Binding are both specified, the Single Node Binding is used.

8.3 Additional Elements

The child elements detailed below provide the ability to attach metadata to form controls.

Instead of supplying such metadata e.g., the label for a form control as inline content of the contained element label, the metadata can be pointed to by using a simple linking attribute src on these elements. Notice that systematic use of this feature can be exploited in internationalizing XForms user interfaces by:

Factoring all human readable messages to a separate resource XML file.
Using URIs into this XML resource bundle within individual label elements
Finally, an XForms implementation could use content negotiation to obtain the appropriate XML resource bundle, e.g., based on the accept-language headers from the client, to serve up the user interface with messages localized to the client's locale.

8.3.1 The filename Element

Binding attributes on optional element filename specify the location in the instance for the parent element upload, when activated, to place the filename for the chosen binary resource. For security reasons, upload must not take action due to any existing value of the node.

Common Attributes: Common, Single Node Binding

In the following example, the user is prompted to select an image. When activated, upload places in mail/attachment either the binary data of the image or a URI for it, depending on the type declared for the mail/attachment. The filename, perhaps "me.jpg", is placed in the attribute node mail/attachment@filename, and the mediatype, perhaps "image/jpeg" in the attribute node mail/attachment@mediatype.

Example:

<upload ref="mail/attachment" mediatype="image/*">
  <label>Select an image to attach</label>
  <filename ref="@filename"/>
  <mediatype ref="@mediatype"/>
</upload>

Linking Attributes: Link to external hint. If the link traversal fails, it is treated as an error (4.5.3 The xforms-link-error Event).

An example of this element is at 10.1.12 The message Element.

8.3.6 The alert Element

The optional element alert provides a convenient way to attach alert or error information to a form control. Rendering of this element is implementation-defined, and there is no default level such as modal or ephemeral for the displayed message.

Common Attributes: Common, Single Node Binding (optional)

Special Attributes:

Linking Attributes: Link to external alert. If the link traversal fails, it is treated as an error (4.5.3 The xforms-link-error Event).

9 XForms User Interface

This chapter covers XForms features for combining form controls into user interfaces.

9.1 The XForms Group Module

All form controls defined in 8 Form Controls are treated as individual units for purposes of visual layout e.g., in XHTML processing. Aggregation of form controls with markup defined in this chapter provides semantics about the relationship among user interface controls; such knowledge can be useful in delivering a coherent UI to small devices. For example, if the user interface needs to be split up over several screens, controls appearing inside the same aggregation would typically be rendered on the same screen or page. The elements and attributes included in this module are:

Element	Attributes	Minimal Content Model
group	Common, UI Common, Single Node Binding (optional)	label?, ((Form Controls)\|group\|switch\|repeat\|UI Common)*

9.1.1 The group Element

The group element is used as a container for defining a hierarchy of form controls. Groups can be nested to create complex hierarchies. A group is considered to be non-relevant if and only if:

the Single Node Binding is expressed and resolves to empty nodeset,
the Single Node Binding is expressed and resolves to a non-relevant instance node,
the group is contained by a non-relevant switch or group (which includes a non-relevant repeat item), or
the group is contained by a non-selected case element of a switch.

All content elements (e.g. form controls, groups, switches, repeats and host language content) within a non-relevant group are handled as non-relevant. When a group becomes non-relevant, it must receive event xforms-disabled and then the XForms action handlers that are listening for events on the non-relevant group must be disabled. When a non-relevant group changes to being relevant, the XForms action handlers that listen for events on the group must become enabled and then the group must receive the event xforms-enabled.

Common Attributes: Common, UI Common, Single Node Binding (optional)

Note:

If a group is non-relevant, then the rendering approach used to signify non-relevance is applied to the entire content of the group.

The optional label element has special significance when it appears as the first element child of group, representing a label for the entire group.

Example:

Grouping Related Controls

<group ref="address">
  <label>Shipping Address</label>
  <input ref="line_1">
    <label>Address line 1</label>
  </input>
  <input ref="line_2">
    <label>Address line 2</label>
  </input>
  <input ref="postcode">
    <label>Postcode</label>
  </input>
</group>

Setting the input focus on a group results in the focus being set to the first form control in the navigation order within that group.

9.2 The XForms Switch Module

This section defines a switch construct that allows the creation of user interfaces where the user interface can be varied based on user actions and events. The elements and attributes included in this module are:

Element	Attributes	Minimal Content Model
switch	Common, UI Common, Single Node Binding (optional)	case+
case	Common, selected (xsd:boolean)	label?, ((Form Controls)\|Action\|group\|switch\|repeat)*
toggle	Common, case (xsd:IDREF)	EMPTY

9.2.1 The switch Element

This element contains one or more case elements, any one of which is rendered at a given time.

Note:

This is separate from XForms relevant processing (see 6.1.4 The relevant Property), which is based on the current state of the XForms Model. As an example, portions of a questionnaire pertaining to the user's automobile may become relevant only if the user has answered in the affirmative to the question 'Do you own a car?'.

The non-relevance of a switch is determined in the same way as it is for group and similarly applies to the entire content. Also, as with group, when a switch becomes non-relevant, it must receive event xforms-disabled and then the XForms action handlers that are listening for events on the non-relevant switch must be disabled. As well, when a non-relevant switch changes to being relevant, the XForms action handlers that listen for events on the switch must become enabled and then the switch must receive the event xforms-enabled.

Common Attributes: Common, UI Common, Single Node Binding (optional)

Example:

switch

<switch>
  <case id="in" selected="true">
    <input ref="yourname">
      <label>Please tell me your name</label>
      <toggle ev:event="DOMActivate" case="out"/>
    </input>
  </case>
  <case id="out" selected="false">
    <html:p>Hello <output ref="yourname" />
      <trigger id="editButton">
        <label>Edit</label>
        <toggle ev:event="DOMActivate" case="in"/>
      </trigger>
    </html:p>
  </case>
</switch>

The above results in the portion of the user interface contained in the first case being displayed initially. This prompts for the user's name; filling in a value and activating the control e.g., by pressing enter results switches to the alternate case, with a read-only output rendering. Activating the trigger labeled "Edit" in turn switches back to the original case.

9.2.2 The case Element

This element encloses markup to be conditionally rendered. The content elements (e.g. form controls, groups, switches, repeats and host language elements) within a non-selected case behave as if they were in a non-relevant group (see 9.1.1 The group Element). Similarly, content elements in a case that becomes selected behave as if they were in a group that has become relevant. The attribute selected determines the initial selected state.

Common Attributes: Common

Special Attributes:

selected: Optional selection status for the case. The default value is "false".

If multiple cases within a switch are marked as selected="true", the first selected case remains and all others are deselected. If none are selected, the first becomes selected.

9.2.3 The toggle Element

This XForms Action selects one possible case from an exclusive list of alternatives in a switch.

This action performs the following:

Dispatches an xforms-deselect event to the currently selected case in the switch containing the identified case.
Adjusts the selected states (not the attribute values) on the affected cases to reflect the new state of the switch containing the identified case.
Dispatches an xform-select event to the case just selected.

Common Attributes: Common, Events

Special Attributes:

case: Required reference to a case element.

Note:

The IDREF obtained from the case attribute may not uniquely identify the desired case if the case element bearing the matching ID resides in a repeating construct such as element repeat. The general method described in 4.7 Resolving ID References in XForms is used to determine the desired run-time case object.

9.3 The XForms Repeat Module

The XForms specification allows the definition of repeating structures such as multiple items within a purchase order. When defining the XForms Model, such higher-level collections are constructed out of basic building blocks; similarly, this section defines user interface construct repeat that can bind to data structures such as lists and collections. The elements and attributes included in this module are:

Element	Attributes	Minimal Content Model
repeat	Common, UI Common, Node Set Binding, startindex (xsd:positiveInteger), number (xsd:nonNegativeInteger)	((Form Controls)\|group\|switch\|repeat)*
itemset	Common, Node Set Binding	label, (value\|copy), (UI Common)*
copy	Common, Single Node Binding (optional)	EMPTY
insert	Common, Events, Node Set Binding, at (XPath Expression), position ("before"\|"after")	EMPTY
delete	Common, Events, Node Set Binding, at (XPath Expression)	EMPTY
setindex	Common, Events, repeat (xsd:IDREF), index (XPath Expression)	EMPTY
(various)	[repeat-nodeset, repeat-bind, repeat-model] (Node Set Binding attributes), repeat-startindex (xsd:positiveInteger), repeat-number (xsd:nonNegativeInteger)	N/A

9.3.1 The repeat Element

This element defines a UI mapping over a homogeneous collection selected by Node Set Binding Attributes. This node-set must consist of contiguous child element nodes, with the same local name and namespace name of a common parent node. The behavior of element repeat with respect to non-homogeneous node-sets is undefined.

For example:

Shopping Cart

<repeat nodeset="/cart/items/item">
  <input ref="." ...>
     <label>...</label>
  </input>
  <html:br/>
</repeat>

Common Attributes: Common, UI Common, Node Set Binding

Special Attributes:

startindex: Optional 1-based initial value of the repeat index. The default value is 1.
number: Optional hint to the XForms Processor as to how many elements from the collection to display.

This element operates over a homogeneous collection by binding the encapsulated user interface controls to each element of the collection. if an element of the collection is non-relevant, then the rendering approach used to signify non-relevance is applied to the associated user interface controls. Attributes on this element specify how many members of the collection are presented to the user at any given time. XForms Actions insert, delete, and setindex can be used to operate on the collection—see 10 XForms Actions. Another way to view repeat processing (disregarding special user interface interactions) is to consider "unrolling" the repeat. The above example is similar to the following (given four item elements in the returned node-set):

Repeat Unrolled

<!-- unrolled repeat -->
  <input ref="/cart/items/item[1]"><label>...</label></input><html:br/>
  <input ref="/cart/items/item[2]"><label>...</label></input><html:br/>
  <input ref="/cart/items/item[3]"><label>...</label></input><html:br/>
  <input ref="/cart/items/item[4]"><label>...</label></input><html:br/>

Homogeneous Collection

<model>
  <instance>
    <my:lines>
      <my:line name="a">
        <my:price>3.00</my:price>
      </my:line>
      <my:line name="b">
        <my:price>32.25</my:price>
      </my:line>
      <my:line name="c">
        <my:price>132.99</my:price>
      </my:line>
      </my:lines>
  </instance>
</model>
  ...
<repeat id="lineset" nodeset="/my:lines/my:line">
  <input ref="my:price">
    <label>Line Item</label>
  </input>
  <input ref="@name">
    <label>Name</label>
  </input>
</repeat>
        
<trigger>
  <label>Insert a new item after the current one</label>
  <action ev:event="DOMActivate">
    <insert nodeset="/my:lines/my:line" at="index('lineset')"
      position="after"/>
    <setvalue ref="/my:lines/my:line[index('lineset')]/@name"/>
    <setvalue ref="/my:lines/my:line[index('lineset')]/price">0.00</setvalue>
  </action>  
</trigger>
          
<trigger>
  <label>remove current item</label>
  <delete ev:event="DOMActivate" nodeset="/my:lines/my:line"
    at="index('lineset')"/>
</trigger>

9.3.2 Creating Repeating Structures Via Attributes

Element repeat enables the creation of user interfaces for populating repeating structures. When using XForms within host languages like XHTML, it is often necessary to create repeating structures within constructs such as table. Thus, one might wish to use element repeat within a table to create the rows of a table, where each row of the table binds to a distinct member of a homogeneous collection. Since html:table doesn't (and probably never will) allow xforms:repeat elements as children, another syntax is needed.

Tables And Repeating Structures

<table>
  <repeat nodeset="...">
    <tr>
      <td>...</td>
      ...
    </tr>
  </repeat>
</table>

More generally, there is a need to integrate repeat behavior into host languages at points where the content model of the host language does not or cannot provide the appropriate extension hooks via modularization. To accommodate this, XForms 1.0 defines an alternative syntax that is functionally equivalent to the repeat element, using the following attributes:

repeat-model
repeat-bind
repeat-nodeset
repeat-startindex
repeat-number

The above attributes are equivalent to the repeat attributes of the same name, but without the prefix repeat-. A host language can include these attributes in the appropriate places to enable repeating constructs. For example, a version of XHTML might use:

Tables And Repeating Structures

<html:table xforms:repeat-nodeset="...">
  <html:tr>
    <html:td><xforms:output ref="..."/></html:td>
  </html:tr>
</html:table>

Which could be validated against an appropriately configured XHTML Schema that includes the XForms Repeat module. Note that what gets repeated is the child elements of the element with the repeat- attributes.

Additionally, when using XForms Action setindex, attribute repeat of type idref can point to any element carrying the repeat attributes. Similarly, when using function index against a repeating structure created via the repeat-attributes, the id of that element can be used as the argument to function index.

9.3.3 The itemset Element

This element allows the creation of dynamic selections within controls select and select1, where the available choices are determined at run-time. The node-set that holds the available choices is specified via the Node Set Binding. As with repeat, this nodeset should refer to a homogeneous collection. Child elements label and value indirectly specify the label and storage values. Notice that the run-time effect of itemset is the same as using element choices with child item elements to statically author the available choices.

For each node of the Node Set Binding, an associated item is created. XForms Actions appearing in the content of an itemset are created within each item element, and the in-scope evaluation context for these XForms Actions is based on the node for which the item was generated as described in Section 7.4 Evaluation Context. An XForms processor must not allow XForms Actions contained by an itemset to handle events on the itemset.

Common Attributes: Common, Node Set Binding

Note:

Whenever a refresh event is dispatched the nodeset is re-evaluated to update the list of available choices.

The following example shows element itemset within control select to specify a dynamic list of ice cream flavors:

Dynamic Choice Of Ice Cream Flavors

<model id="cone">
  <instance>
    <my:icecream>
      <my:order/>
    </my:icecream>
  </instance>
</model>
<model id="flavors">
  <instance>
    <my:flavors>
      <my:flavor type="v">
        <my:description>Vanilla</my:description>
      </my:flavor>
      <my:flavor type="s">
        <my:description>Strawberry</my:description>
      </my:flavor>
      <my:flavor type="c">
        <my:description>Chocolate</my:description>
      </my:flavor>
    </my:flavors>
  </instance>
</model>
<!-- user interaction markup -->
<select model="cone" ref="my:order">
  <label>Flavors</label>
  <itemset model="flavors" nodeset="/my:flavors/my:flavor">
    <label ref="my:description"/>
    <copy ref="my:description"/>
  </itemset>
</select>
          
<!-- For all three items selected, this example produces instance data like
     <my:icecream>
       <my:order>
	 <my:description>Vanilla</my:description>
	 <my:description>Strawberry</my:description>
	 <my:description>Chocolate</my:description>    
       </my:order>
     </my:icecream>
-->

9.3.4 The copy Element

Structurally, this element is similar to 8.2.3 The value Element. It differs in that it can only be used within itemset, and that it works with subtrees of instance data rather than simple values.

Common Attributes: Common, Single Node Binding (optional)

When an item becomes selected, the following rules apply:

The target node, selected by the binding attributes on the list form control, must be an element node, otherwise an exception results (4.5.1 The xforms-binding-exception Event).
The element node associated with the item, selected by the binding attributes on copy, is deep copied as a child of the target node.
A full computational dependency rebuild is done.

When an item becomes unselected, the following rules apply:

The target node, selected by the binding attributes on the list form control, must be an element node, otherwise an exception results (4.5.1 The xforms-binding-exception Event).
The child element node associated with the item, selected by the binding attributes on copy, is deleted.
A full computational dependency rebuild.

9.3.5 The insert Element

This action is used to insert new entries into a homogeneous collection, e.g., a set of items in a shopping cart. Attributes of action insert specify the insertion in terms of the collection in which a new entry is to be inserted, and the location within that collection where the new node will appear. The new node is created by cloning the final member of the homogeneous collection. In this process, nodes of type xsd:ID are modified to remain as unique values in the instance data.

Common Attributes: Common, Events, Node Set Binding

Special Attributes:

at: Required XPath expression evaluated to determine insert location.
position: Required selector ("before" or "after") of insert before/after behavior.

The rules for insert processing are as follows:

The homogeneous collection to be updated is determined by evaluating the Node Set Binding. if the collection is empty, the insert action has no effect.
The node-set binding identifies a homogeneous collection in the instance data. The final member of this collection is cloned to produce the node that will be inserted. Finally, this newly created node is inserted into the instance data at the location specified by attributes position and at.
Attribute at is evaluated to determine the insertion index – a numerical value that is the index into the node-set. The attribute at is evaluated with the first node in document order from the node set binding as the context node, the size of the node set binding as the context size and 1 as the context position. Attribute position specifies whether the new node is inserted before or after this index.
The rules for selecting the index are as follows:
1. The return value of the XPath expression in attribute at is processed according to the rules of the XPath function round(). For example, the literal 1.5 becomes 2, and the literal 'string' becomes NaN.
2. If the result is NaN, the insert appends to the end of the node-set.
3. If the resulting index is outside the valid range of the node-set, it is replaced with either 1 or the size of the node-set, whichever is closer.
The index for any repeating sequence that is bound to the homogeneous collection where the node was added is updated to point to the newly added node. The indexes for inner nested repeat collections are re-initialized to startindex.
If the insert is successful, the event xforms-insert is dispatched.

This action results in the insertion of newly created data nodes into the XForms instance data. Such nodes are constructed as defined in the initialization section of the processing model—see 4.2 Initialization Events. As an example, this causes the instantiation of the necessary user interface for populating a new entry in the underlying collection when used in conjunction with repeating structures.

Note:

This action has special deferred update behavior.

An example of using insert with a repeating structure is located at 9.3.1 The repeat Element. Note that XForms Action setvalue can be used in conjunction with insert to provide initial values for the newly inserted nodes.

9.3.6 The delete Element

This action deletes nodes from the instance data.

Common Attributes: Common, Events, Node Set Binding

Special Attributes:

at: Required XPath expression evaluated to determine delete location.

The rules for delete processing are as follows:

The homogeneous collection to be updated is determined by evaluating the Node Set Binding. If the collection is empty, the delete action has no effect.
The n-th element node is deleted from the instance data, where n represents the number returned from node-set index evaluation, defined in 9.3.5 The insert Element. If no nth node exists, the operation has no effect.
The index should point to the same node after a delete as it did before the delete except:
- When the last remaining item in the collection is removed, the index position becomes 0.
- When the index was pointing to the deleted node, which was the last item in the collection, the index will point to the new last node of the collection and the index of inner repeats is reinitialized.
- When the index was pointing to the deleted node, which was not the last item in the collection, the index position is not changed and the index of inner repeats is re-initialized.
To re-initialize a repeat index means to change its value to be equal to startindex, or to the size of the homogeneous collection if it contains less than startindex items.
If the delete is successful, the event xforms-delete is dispatched.

This action results in deletion of nodes in the instance data.

Note:

This action has special deferred update behavior.

An example of using delete with a repeating structure is located at 9.3.1 The repeat Element.

9.3.7 The setindex Element

This action marks a specific item as current in a repeating sequence (within 9.3.1 The repeat Element).

Common Attributes: Common, Events

Special Attributes:

repeat: Required reference to a repeating element.
index: Required XPath expression that evaluates to a 1-based offset into the sequence. The evaluation context is determined in the same manner as the evaluation context for a Single-Node Binding (see 7.4 Evaluation Context).

If the selected index is 0 or less, an xforms-scroll-first event is dispatched and the index is set to 1. If the selected index is greater than the index of the last repeat item, an xforms-scroll-last event is dispatched and the index is set to that of the last item. if the index evaluates to NaN the action has no effect. The indexes for inner nested repeat collections are re-initialized to startindex. The implementation data structures for tracking computational dependencies are rebuilt or updated as a result of this action.

Note:

The IDREF from the repeat attribute may not uniquely identify the desired repeat if the repeat element bearing the matching ID resides within the content of another repeat. The general method described in 4.7 Resolving ID References in XForms is used to determine the desired run-time repeat object.

9.3.8 Repeat Processing

The markup contained within the body of element repeat specifies the user interface to be generated for each member of the underlying collection. During user interface initialization (see 4.2.2 The xforms-model-construct-done Event), the following steps are performed for repeat:

The Node Set Binding is evaluated to locate the homogeneous collection to be operated on by this repeat.
The index for this repeating structure is initialized to the value of startindex. if the initial startindex is less than 1 it defaults to 1. If the index is greater than the initial node-set then it defaults to the size of the node-set.
User interface as specified by the repeat is generated for the requisite number of members of the collection as specified by attributes on element repeat.

The processing model for repeating structures uses an index that points to the current item in the instance data. This repeat index is accessed via XForms function index 7.8.5 The index() Function and manipulated via XForms Action setindex 9.3.7 The setindex Element. This index is used as a reference point for insert and delete operations. Notice that the contained XForms form controls inside element repeat do not explicitly specify the index of the collection entry being populated. This is intentional; it keeps both authoring as well as the processing model simple.

The binding expression attached to the repeating sequence returns a node-set of the collection being populated, not an individual node. Within the body of element repeat, binding expressions are evaluated with a context node of the node determined by the index. Repeat processing uses XPath expressions to address the collection over which element repeat operates.

The form controls appearing inside repeat need to be suitable for populating individual items of the collection. A simple but powerful consequence of the above is that if the XForms Model specifies nested collections, then a corresponding user interface can nest repeat elements.

9.3.9 Nested Repeats

It is possible to nest repeat elements to create more powerful user interface for editing structured data. G.2 Editing Hierarchical Bookmarks Using XForms is an example of a form using nested repeats to edit hierarchical data consisting of bookmarks within multiple sections. Consider the following insert statement that appears as part of that example.

Repeat Index and Nested Repeats

<xforms:insert nodeset="/bookmarks/section[index('repeatSections')]/bookmark"
               at="index('repeatBookmarks')"
               position="after"/>

The above insert statement is used in that example to add new bookmark entries into the currently selected section. The inner (nested) repeat operates on bookmarks in this selected section; The index—as returned by XForms function index—for this inner repeat starts at 1. Hence, after a new empty section of bookmarks is created and becomes current, the first insert bookmark operation adds the newly created bookmark at the front of the list.

9.3.10 User Interface Interaction

Element repeat enables the binding of user interaction to a homogeneous collection. The number of displayed items might be less than the total number available in the collection. In this case, the presentation would render only a portion of the repeating items at a given time. For example, a graphical user interface might present a scrolling table. The current item indicated by the repeat index should be made available to the user at all times, for example, not allowed to scroll out of view. The XForms Actions enumerated at 10 XForms Actions may be used within event listeners to manipulate the homogeneous collection being populated by scrolling, inserting, and deleting entries.

Notice that the markup encapsulated by element repeat acts as the template for the user interface that is presented to the user. As a consequence, statically authored IDREF attributes must be interpreted based on a combination of repeat indexes and where the IDREF attributes appear relative to the element bearing the matching ID. Based on the IDREF resolution rules given in 4.7 Resolving ID References in XForms, it is possible to toggle the case of a switch even when it is within one or more repeat elements. Similarly, it is possible to set the focus to controls and dispatch events to elements that are within one or more repeat elements.

If the focus is transferred to a control within a repeat by any means, such as by an XForms action or by user interaction, the index of the repeat is changed to indicate the item of the homogeneous collection that contains the control. This effect is recursive; the index of each containing repeat is adjusted appropriately.

10 XForms Actions

This chapter defines an XML Events-based [XML Events] common set of actions that can be invoked in response to events.

Note:

XForms itself defines no method for script-based event handling. The definition of such facilities is a responsibility of the hosting language.

10.1 The XForms Action Module

All form controls defined in this specification have a set of common behaviors that encourage consistent authoring and look and feel for XForms-based applications. This consistency comes from attaching a common set of behaviors to the various form controls. In conjunction with the event binding mechanism provided by XML Events, these handlers provide a flexible means for forms authors to specify event processing at appropriate points within the XForms user interface. XForms Actions are declarative XML event handlers that capture high-level semantics. As a consequence, they significantly enhance the accessibility of XForms-based applications in comparison to previous Web technologies that relied exclusively on scripting.

The elements and attributes included in this module are:

Element	Attributes	Minimal Content Model
action	Common, Events	(Action)+
dispatch	Common, Events, name (xsd:NMTOKEN), target (xsd:IDREF), bubbles (xsd:boolean), cancelable (xsd:boolean)	EMPTY
rebuild	Common, Events, model (xsd:IDREF)	EMPTY
recalculate	Common, Events, model (xsd:IDREF)	EMPTY
revalidate	Common, Events, model (xsd:IDREF)	EMPTY
refresh	Common, Events, model (xsd:IDREF)	EMPTY
setfocus	Common, Events, control (xsd:IDREF)	EMPTY
load	Common, Events, Single Node Binding (optional), resource (xsd:anyURI), show ("new" \| "replace")	EMPTY
setvalue	Common, Events, Single Node Binding, value (XPath Expression)	PCDATA
send	Common, Events, submission (xsd:IDREF)	EMPTY
reset	Common, Events, model (xsd:IDREF)	EMPTY
message	Common, Events, Single Node Binding (optional), Linking, level ("ephemeral" \| "modeless" \| "modal")	(PCDATA\|UI Inline)*

This module also defines the content set "Action", which includes the following elements (of these, toggle comes from the XForms Switch module, and insert, delete, and setindex come from the XForms Repeat module):

(action|dispatch|rebuild|refresh|recalculate|revalidate|setfocus|
 load|setvalue|send|reset|message|toggle|insert|delete|setindex)*

Additionally, this module defines the attribute group "XML Events", which includes all of the "global" attributes defined in that specification ([XML Events]).

The following example shows how events can be used:

Action Syntax

<xforms:trigger>
  <xforms:label>Reset</xforms:label>
  <xforms:reset ev:event="DOMActivate" model="thismodel"/>
</xforms:trigger>

This example recreates the behavior of the HTML reset control, which this specification does not define as an independent form control.

For each built-in XForms Action, this chapter lists the following:

Name
Common Attributes
Special Attributes
Description of behavior

All elements defined in this chapter explicitly allow global attributes from the XML Events namespace, and apply the processing defined in that specification in section 2.3 [XML Events].

An outermost action handler is an action that is activated when the XForms processor is not executing any other action handlers.

An inner action handler is an action that is activated when the XForms processor is executing the declared actions of an outermost action handler. An inner action handler may be within the content of the outermost action handler, or it may be executed as the response to an event dispatched while performing all of the actions initiated by the outermost action handler.

Deferred Updates: Sequences of one or more XForms Actions have a deferred effect on XForms model and user interface processing . Implementations are free to use any strategy to accomplish deferred updates, but the end result must be as follows: Instance data changes performed by a set of actions do not result in immediate computation dependency rebuilding, recalculation, revalidate and form control refreshing until the termination of the outermost action handler, as described here. Each XForms model can be thought of as having a set of deferred update Boolean flags, initially false at the start of an outermost action handler, to indicate whether each of the actions rebuild, recalculate, revalidate, and refresh are required for that model upon termination of the outermost action handler.

Execution of an outermost action handler begins by setting the XForms processor into the state of executing an outermost action handler. The outermost action handler is then performed, which may include the execution of inner action handlers. Finally, the XForms processor is set into the state of not executing an outermost action handler and then the deferred update is performed for each model. The deferred update behavior for a model consists of examining each deferred update Boolean flag in the order of rebuild, recalculate, revalidate, and refresh, and for each true flag, set the flag to false and then dispatch the proper event to the model for that deferred update flag (i.e. dispatch xforms-rebuild for a true rebuild flag, xforms-recalculate for a true recalculate flag, xforms-revalidate for a true revalidate flag, and xforms-refresh for a true refresh flag).

Note:

The XForms processor is not considered to be executing an outermost action handler at the time that it performs deferred update behavior for XForms models. Therefore, event handlers for events dispatched to the user interface during the deferred refresh behavior are considered to be new outermost action handler.

Actions that directly invoke rebuild, recalculate, revalidate, or refresh always have an immediate effect, and clear the corresponding deferred update flag. The XForms Actions in this category are:

rebuild
recalculate
revalidate
refresh

XForms Actions that change the tree structure of instance data result in setting all four deferred update flags to true for the model over which they operate. The XForms Actions in this category are:

insert
delete

XForms Actions that change only the value of an instance node results in setting the deferred update flags for recalculate, revalidate, and refresh to true and making no change to the deferred update flag for rebuild for the model over which they operate. The XForms Actions in this category are:

setvalue

Finally, the reset action clears all of the deferred update flags for a model. Similarly, if the default processing of xforms-submit replaces instance data in a model, then the deferred update flags for that model are cleared immediately before the behaviors are peformed for xforms-rebuild, xforms-recalculate, xforms-revalidate, and xforms-refresh.

10.1.1 The action Element

This action causes its child actions to be invoked in the order that they are specified in the document.

Common Attributes: Common, Events

Grouping Actions

<trigger>
  <label>Click me</label>
  <action ev:event="DOMActivate">
    <reset model="thismodel"/>
    <setvalue ref="."/>
  </action>
</trigger>

10.1.2 The dispatch Element

This action dispatches an XForms Event to a specific element identified by the target attribute. Two kinds of event can be dispatched:

Predefined XForms events (i.e., xforms-event-name), in which case the bubbles and cancelable attributes are ignored and the standard semantics as defined in 4 Processing Model apply.
An event created by the XForms author with no predefined XForms semantics and as such not handled by default by the XForms Processor.

Common Attributes: Common, Events

Special Attributes:

name: Required name of the event to dispatch.
target: Required reference to the event target.
bubbles: Optional boolean indicating if this event bubbles—as defined in [DOM2 Events]. The default value is true for a custom event. For predefined events, this attribute has no effect.
cancelable: Optional boolean indicating if this event is cancelable—as defined in [DOM2 Events]. The default value is true for a custom event. For predefined events, this attribute has no effect.

Note:

The IDREF obtained from the target attributemay not uniquely identify the desired target object if the element bearing the matching ID resides in a repeating construct such as element repeat. The general method described in 4.7 Resolving ID References in XForms is used to determine the desired target object.

10.1.3 The rebuild Element

This action causes the processing of xforms-rebuild to happen, bypassing the normal event flow (i.e. the behavior occurs without dispatching the xforms-rebuild event). This action results in the XForms Processor rebuilding any internal data structures used to track computational dependencies among instance data nodes —see 4.3.7 The xforms-rebuild Event.

Common Attributes: Common, Events

Special Attributes:

model: Optional XForms Model selector, as defined in 3.2.3 Single-Node Binding Attributes. If this attribute is omitted, then the default is the model associated with the in-scope evaluation context node.

Note:

This action has special deferred update behavior.

10.1.4 The recalculate Element

This action causes the processing of xforms-recalculate to happen, bypassing the normal event flow (i.e. the behavior occurs without dispatching the xforms-recalculate event). As a result, instance data nodes whose values need to be recalculated are updated as specified in the processing model—see 4.3.6 The xforms-recalculate Event.

Common Attributes: Common, Events

Special Attributes:

model: Optional XForms Model selector, as defined in 3.2.3 Single-Node Binding Attributes. If this attribute is omitted, then the default is the model associated with the in-scope evaluation context node.

Note:

This action has special deferred update behavior.

10.1.5 The revalidate Element

This action causes the processing of xforms-revalidate to happen, bypassing the normal event flow (i.e. the behavior occurs without dispatching the xforms-revalidate event). This results in the instance data being revalidated as specified by the processing model—see 4.3.5 The xforms-revalidate Event.

Common Attributes: Common, Events

Special Attributes:

model: Optional XForms Model selector, as defined in 3.2.3 Single-Node Binding Attributes. If this attribute is omitted, then the default is the model associated with the in-scope evaluation context node.

Note:

This action has special deferred update behavior.

10.1.6 The refresh Element

This action causes the processing of xforms-refresh to happen, bypassing the normal event flow (i.e. the behavior occurs without dispatching the xforms-refresh event). This action results in the XForms user interface being refreshed, and the presentation of user interface controls being updated to reflect the state of the underlying instance data—see 4.3.4 The xforms-refresh Event.

Common Attributes: Common, Events

Special Attributes:

model: Optional XForms Model selector, as defined in 3.2.3 Single-Node Binding Attributes. If this attribute is omitted, then the default is the model associated with the in-scope evaluation context node.

Note:

This action has special deferred update behavior.

10.1.7 The setfocus Element

This action dispatches an xforms-focus event (4.3.2 The xforms-focus Event) to the element identified by attribute control. Note that this event is implicitly invoked to implement XForms accessibility features such as accesskey.

Common Attributes: Common, Events

Special Attributes:

control: Required reference to a form control.

Setting focus to a repeating structure sets the focus to the repeat item represented by the repeat index.

Note:

The IDREF obtained from the control attribute may not uniquely identify the desired form control if the element bearing the matching ID resides in a repeating construct such as element repeat. The general method described in 4.7 Resolving ID References in XForms is used to determine the desired form control.

10.1.8 The load Element

This action traverses the specified link.

Common Attributes: Common, Events, Single-Node Binding (optional)

Special Attributes:

resource: Optional. Link to external resource to load, defined as an [XLink 1.0] link between this element and the remote resource indicated. No XLink actuate value is defined, since control of actuation is defined by XML Events. The XLink show value depends on the show attribute. If the link traversal fails, it is treated as an error (4.5.3 The xforms-link-error Event).
show: Optional link behavior specifier. if this attribute is missing, a default value of "replace" is assumed.

Either the Single-Node Binding attributes, pointing to a URI in the instance data, or the resource attribute is required. If both the Single-Node Binding and the resource attributeare present, the action has no effect. This action has no effect if the Single-Node Binding is present and does not select an instance data node.

Possible values for attribute show have the following processing for the document (or portion of a document) reached by traversing the link:

new: The document is loaded into a new presentation context, e.g., a new window. Form processing in the original window continues.
replace: The document is loaded into the current window. Form processing is interrupted, exactly as if the user had manually requested navigating to a new document.

10.1.9 The setvalue Element

This action explicitly sets the value of the specified instance data node. This action has no effect if the Single-Node Binding does not select an instance data node.

Common Attributes: Common, Events, Single Node Binding

Special Attributes:

value: Optional XPath expression to evaluate, with the result stored in the selected instance data node. The evaluation context for this XPath expression is the result from the Single Node Binding.

The element content of setvalue specifies the literal value to set; this is an alternative to specifying a computed value via attribute value. The following two examples contrast these approaches:

setvalue with Expression

<setvalue bind="put-here" value="a/b/c"/>

This causes the string value at a/b/c in the instance data to be placed on the single node selected by the bind element with id="put-here".

setvalue with Literal

<setvalue bind="put-here">literal string</setvalue>

This causes the value "literal string" to be placed on the single node selected by the bind element with id="put-here".

If neither a value attribute nor text content are present, the effect is to set the value of the selected node to the empty string (""). If both are present, the value attribute is used.

All strings are inserted into the instance data as follows:

Element nodes: If the element has any child text nodes, the first text node is replaced with one corresponding to the new value. If no child text nodes are present, a text node is created, corresponding to the new value, and appended as the first child node.
Attribute nodes: The string-value of the attribute is replaced with a string corresponding to the new value.
Text nodes: The text node is replaced with a new one corresponding to the new value.
Namespace, processing instruction, comment, and the XPath root node: behavior is undefined.

Note:

This action has special deferred update behavior.

10.1.10 The send Element

This action initiates submit processing by dispatching an xforms-submit event. Processing of event xforms-submit is defined in the processing model—see 4.3.9 The xforms-submit Event.

Common Attributes: Common, Events

Special Attributes:

submission: Required reference to a submission element.

Note:

This XForms Action is a convenient way of expressing the following:

<dispatch target="mysubmitinfo" name="xforms-submit"/>

10.1.11 The reset Element

This action initiates reset processing by dispatching an xforms-reset event to the specified model. Processing of event xforms-reset is defined in the processing model—see 4.3.8 The xforms-reset Event.

Common Attributes: Common, Events

Special Attributes:

model: Optional XForms Model selector, as defined in 3.2.3 Single-Node Binding Attributes. If this attribute is omitted, then the default is the model associated with the in-scope evaluation context node.

Note:

This action has special deferred update behavior.

10.1.12 The message Element

This action encapsulates a message to be displayed to the user.

Common Attributes: Common, Events, Single Node Binding (optional)

Special Attributes:

Linking Attributes: Link to external message. If the link traversal fails, it is treated as an error (4.5.3 The xforms-link-error Event).
level: Required message level identifier, one of ("ephemeral"|"modeless"|"modal"|QNameButNotNCNAME). This specification does not define behavior for QName values.

The user interface for the message action is considered to be created at the time the action occurs. If the message is obtained from the inline content of the message action, then the output of any output controls in the message content is determined based on the instance data available when the message action occurs. For example, the following example displays the message Hello, world! as the form starts up:

<model>
     <instance xmlns="">
         <data>
             <name>John</name>
         </data>
     </instance>
   
     <action ev:event="xforms-ready">
         <setvalue ref="name">world</setvalue>
         <message level="modal">Hello, <output ref="name"/>!</message>
  ...</action>
</model>

In this example, the message includes the latest user input even though other form controls not in the message action are not guaranteed to be updated until the end of the xforms-refresh event processing:

<input ref="birthday">
     <label>Enter birthday:</label>
     <message ev:event="xforms-invalid"><output ref="."/> isn't a valid birthday</message>
</input>

Note:

Due to deferred update behavior, if a message action is preceded in an action sequence by other actions that change instance nodes, and the message references nodes that are computationally dependent on the changed nodes, then the form author should invoke the recalculate action before the message action.

A graphical browser might render a modal message as follows:

<model>
  <message level="modal" ev:event="xforms-ready">This is not a drill!</message>
  ...
</model>

An alert popup, with a helpful error message.

A modeless message is the foundation for displaying a help message, which a graphical browser might render as follows:

<secret ref="/login/password">
  <label>Password</label>
  <help>Have you forgotten your password? Simply call 1-900-555-1212 and have
        a major credit card handy.</help>
</secret>

A password entry form control, with a popup window below, displaying instructions for retrieving a forgotten password

An ephemeral message is the foundation for displaying a hint message, which a graphical browser might render as follows:

<input ref="po/address/street1">
  <label>Street</label>
  <hint>Please enter the number and street name</hint>
</input>

An average-looking text entry form control, with a mouse pointer visible and a tooltip below, reading 'Please enter the number and street name'

10.1.13 Actions `insert`, `delete` and `setindex`

In addition to the action handlers detailed in this chapter, XForms defines three actions as part of the XForms Repeat module: 9.3.5 The insert Element, 9.3.6 The delete Element, and 9.3.7 The setindex Element.

11 Submit

XForms is designed to gather instance data, serialize it into an external representation, and submit it with a protocol. XForms defines a set of options for serialization and submission. The following sections define the processing of instance data for submission, and the behavior for the serialization and submission options.

11.1 The xforms-submit Event

Submission begins with the default action for a xforms-submit event.

Target: submission

Bubbles: Yes

Cancelable: Yes

Context Info: None

Under no circumstances may more than a single concurrent submit process be under way for a particular XForms submission. From the start of the default action of xforms-submit, until the completion of the default action for xforms-submit-done or xforms-submit-error, the default action for subsequent xforms-submit events is to do nothing.

Otherwise, the default action for this event results in the following steps:

The data model is updated. Specifically, if the deferred update rebuild flag is set for the model containing this submission, then the rebuild operation is performed without dispatching an event to invoke the operation. Then, if the deferred update recalculate flag is set for the model containing this submission, then the recalculate operation is performed without dispatching an event to invoke the operation. Performing the operations clears the flags.
A node from the instance data is selected, based on attributes on the submission element. If the attributes of submission select an empty nodeset, a non-relevant node or a non-element node, then submission processing is stopped after dispatching event xforms-submit-error. Otherwise, the indicated node and all nodes for which it is an ancestor are considered for the remainder of the submit process. Any node which is considered not relevant as defined in 6.1.4 The relevant Property is removed.
All selected instance data nodes are checked for validity according to the definition in 4.3.5 The xforms-revalidate Event (no notification events are marked for dispatching due to this operation). Any selected instance data node that is required but empty or found to be invalid stops submission processing after dispatching event xforms-submit-error.
Selected instance data is serialized according to the rules stated at 11.2 Submission Options.
Serialized instance data is submitted using the protocol indicated by the rules stated at 11.2 Submission Options.
The response returned from the submission is applied as follows:
- For a success response including a body, when the value of the replace attribute on element submission is "all", the event xforms-submit-done is dispatched, and submit processing concludes with entire containing document being replaced with the returned body.
- For a success response including a body of an XML media type (as defined by the content type specifiers in [RFC 3023]), when the value of the replace attribute on element submission is "instance", the response is parsed as XML. An xforms-link-exception (4.5.2 The xforms-link-exception Event) occurs if the parse fails. If the parse succeeds, then all of the internal instance data of the instance indicated by the instance attribute setting is replaced with the result. Once the XML instance data has been replaced, the rebuild, recalculate, revalidate and refresh operations are performed on the model, without dispatching events to invoke those four operations. This sequence of operations affects the deferred update behavior by clearing the deferred update flags associated with the operations performed. Submit processing then concludes after dispatching xforms-submit-done.
- For a success response including a body of a non-XML media type (i.e. with a content type not matching any of the specifiers in [RFC 3023]), when the value of the replace attribute on element submission is "instance", nothing in the document is replaced and submit processing concludes after dispatching xforms-submit-error.
- For a success response including a body, when the value of the replace attribute on element submission is "none", submit processing concludes after dispatching xforms-submit-done.
- For a success response not including a body, submit processing concludes after dispatching xforms-submit-done.
- Behaviors of other possible values for attribute replace are not defined in this specification.
- For an error response nothing in the document is replaced, and submit processing concludes after dispatching xforms-submit-error.

11.2 Submission Options

The XForms Model specifies a submission element containing the following attributes that affect serialization and submission. This section summarizes the behaviors for the allowable values of these attributes, and introduces the following sections that define the behavior for serialization and submission. (See 3.3.3 The submission Element for additional submission attributes that affect serialization.)

action (xsd:anyURI)
method (xsd:string, enumerated below)

For the URI scheme of action, XForms normatively defines a binding to HTTP/1.1 [RFC 2616].

Note:

Other bindings, in particular to the URI scheme "mailto:" may, and the schemes "https:" and "file:" should, be supported. Bindings to these schemes are not normatively defined in XForms. Implementations that choose to provide a binding to these schemes should pay particular attention to privacy and security concerns. Within the "http:" and "https:" schemes, form creators are encouraged to follow the finding of the W3C Technical Architecture Group on when to use the GET method: [TAG Finding 7]

The method attribute determines the serialization format, and the URI scheme used in the action attribute determines the submit protocol, according to the following table:

URI scheme	`method`	Serialization	Submission
http https mailto	"post"	`application/xml`	HTTP POST or equivalent
http https file	"get"	`application/x-www-form-urlencoded`	HTTP GET or equivalent
http https file	"put"	`application/xml`	HTTP PUT or equivalent
http https mailto	"multipart-post"	`multipart/related`	HTTP POST or equivalent
http https mailto	"form-data-post"	`multipart/form-data`	HTTP POST or equivalent
http https mailto	"urlencoded-post"	`application/x-www-form-urlencoded`	HTTP POST or equivalent
(any)	any other QNAME with no prefix	N/A	N/A
(any)	any QNAME with a prefix	implementation-defined	implementation-defined

Note:

Foreign-namespaced attributes are allowed on element submission, but no behavior is defined by XForms 1.0.

11.3 Serialization as application/xml

This format permits the expression of the instance data as XML that is straightforward to process with off-the-shelf XML processing tools. In addition, this format is capable of submission of binary content.

The steps for serialization are as follows:

An XML document is produced following the rules of the XML output method defined in [XSLT 1.0] section 16 and 16.1, using the values supplied as attributes of the submission element.
1. Handling of namespace nodes: The default behavior is that every namespace node is serialized according to the rules of the XML output method, so that at least one namespace declaration appears in the serialized XML for each in-scope namespace. Additional inherited namespaces are declared on the root element of the serialized XML. If, however, attribute includenamespaceprefixes on element submission is present, then all namespace declarations not visibly utilized in the instance data (as defined in [Exc-C14N]) and the default namespace if it is empty are excluded from the root element serialization, unless the corresponding namespace prefix is listed in the includenamespaceprefixes attribute. The special value #default represents the default namespace.
2. Mediatype: By default, the mediatype of the serialized XML instance is application/xml, but can be changed to a compatible type using element submission attribute mediatype. Authors should ensure that the type specified is compatible with application/xml.

11.4 Serialization as multipart/related

This format is intended for integration of XForms into environments that involve large amounts of binary data where the inclusion of the data as xsd:base64Binary or xsd:hexBinary is undesirable.

In this format, XML instance data is serialized as one part of the [RFC 2387] multipart/related message, using the rules as described in 11.3 Serialization as application/xml. Binary content from xsd:anyURI instance nodes populated by the upload (see 8.1.6 The upload Element) control is serialized in separate parts of the [RFC 2387] multipart/related message.

This format follows the rules of multipart/related MIME data streams for in [RFC 2387], with specific requirements of this serialization listed below:

multipart/related message header requirements:
- Must contain a type parameter of the mediatype of the serialized XML instance.
- Must contain a start parameter referring to the Content-ID first body part (root).
First body part (root) requirements:
- Must have Content-Type parameter of the type specified by the submission mediatype attribute.
- Content is serialized by the rules at 11.3 Serialization as application/xml.
Subsequent part requirements:
- One part for each node with a datatype of xsd:anyURI populated by upload with:
  - A Content-Type header that represents the type of the attachment if known, otherwise application/octet-stream.
  - A Content-Transfer-Encoding header.
  - A Content-ID header whose value matches the URI in the associated instance data node.
  - The binary content associated with the URI, serialized according to the Content-Transfer-Encoding heading.

multipart/related

Content-Type: multipart/related; boundary=f93dcbA3; type=application/xml; start="<980119.X53GGT@example.com>"
Content-Length: xxx

--f93dcbA3
Content-Type: application/xml; charset=UTF-8
Content-ID: <980119.X53GGT@example.com>

<?xml version="1.0"?>
<uploadDocument>
  <title>My Proposal</title>
  <author>E. X. Ample</author>
  <summary>A proposal for a new project.</summary>
  <notes image="cid:980119.X17AXM@example.com">(see handwritten region)</notes>
  <keywords>project proposal funding</keywords>
  <readonly>false</readonly>
  <filename>image.png</filename>
  <content>cid:980119.X25MNC@example.com</content>
</uploadDocument>
--f93dcbA3
Content-Type: image/png
Content-Transfer-Encoding: binary
Content-ID: <980119.X25MNC@example.com>

...Binary data here...
--f93dcbA3
Content-Type: image/png
Content-Transfer-Encoding: binary
Content-ID: <980119.X17AXM@example.com>

...Binary data here...
--f93dcbA3--

11.5 Serialization as multipart/form-data

This format is for legacy compatibility to permit the use of XForms clients with [RFC 2388] servers. This method is suitable for the persistence of binary content. Contextual path information, attribute values, namespaces and namespace prefixes are not preserved. As a result, different elements might serialize to the same name.

Note:

Existing HTML user agents fail to encode special characters (such as double quotes) and non-ASCII characters in the Content-Disposition: form-data name and filename parameters. Since this serialization method is supported for legacy applications only, new applications should use application/xml or multipart/related.

This format follows the rules for multipart/form-data MIME data streams in [RFC 2388], with specific requirements of this serialization listed below:

Each element node is visited in document order.
Each element that has exactly one text node child is selected for inclusion.
Element nodes selected for inclusion are as encoded as Content-Disposition: form-data MIME parts as defined in [RFC 2387], with the name parameter being the element local name.
Element nodes of any datatype populated by upload are serialized as the specified content and additionally have a Content-Disposition filename parameter, if available.
The Content-Type must be text/plain except for xsd:base64Binary, xsd:hexBinary, and derived types, in which case the header represents the media type of the attachment if known, otherwise application/octet-stream. If a character set is applicable, the Content-Type may have a charset parameter.

Example:

multipart/form-data

Content-Type: multipart/form-data; boundary=AaB03x
Content-Length: xxx
        
--AaB03x
Content-Disposition: form-data; name="document"; filename="b.txt"
Content-Type: text/plain; charset=iso-8859-1
This is a file.
It has two lines.
--AaB03x
Content-Disposition: form-data; name="title"
A File
--AaB03x
Content-Disposition: form-data; name="summary"
This is my file
file test
--AaB03x--

11.6 Serialization as application/x-www-form-urlencoded

This format represents an extension of the [XHTML 1.0] form content type application/x-www-form-urlencoded with specific rules for encoding non-ASCII and reserved characters.

This format is not suitable for the persistence of binary content. Therefore, it is recommended that forms capable of containing binary content use another serialization method.

The steps for serialization are as follows:

Each element node is visited in document order. Each element that has one text node child is selected for inclusion. Note that attribute information is not preserved.
Element nodes selected for inclusion are encoded as EltName=value, where = is a literal character, EltName represents the element local name, and value represents the contents of the text node. The separator character {sep} from the separator attribute on submission is used between pairs of encoded name/value pairs, e.g. EltName1=value1{sep}EltName2=value2{sep}EltName3=value3. Note that contextual path information is not preserved, nor are namespaces or namespace prefixes. As a result, different elements might serialize to the same name.
- The encoding of EltName and value are as follows: space characters are replaced by +, and then non-ASCII and reserved characters (as defined by [RFC 2396] as amended by subsequent documents in the IETF track) are escaped by replacing the character with one or more octets of the UTF-8 representation of the character, with each octet in turn replaced by %HH, where HH represents the uppercase hexadecimal notation for the octet value and % is a literal character. Line breaks are represented as "CR LF" pairs (i.e., %0D%0A).
All such encodings are concatenated, maintaining document order.

Example:

application/x-www-form-urlencoded

GivenName=Ren%C3%A9

This format consists of simple name-value pairs.

<PersonName title="Mr">
  <GivenName>René</GivenName>
</PersonName>

Here is the instance data for the above example. Note that very little of the data is preserved. Authors desiring greater data integrity should select a different serialization format.

11.7 The post, multipart-post, form-data-post, and urlencoded-post Submit Methods

These submit methods represent HTTP POST or the equivalent concept (such as a mail message). The serialized form data is delivered as the message body.

11.8 The put Submit Method

This submit method represents HTTP PUT or the equivalent concept (such as writing to a local file). The serialized form data is delivered as the message body.

11.9 The get Submit Method

This submit method represents HTTP GET or the equivalent concept. The serialized form data is delivered as part of the URI that is requested during the submit process.

This method is not suitable for submission of forms that are intended to change state or cause other actions to take place at the server. See [RFC 2616] for recommended uses of HTTP GET.

The URI is constructed as follows:

The submit URI from the action attribute is examined. If it does not already contain a ? (question mark) character, one is appended. If it does already contain a question mark character, then a separator character from the attribute separator is appended.
The serialized form data is appended to the URI.

No message body is sent with the request.

12 Conformance

12.1 Conformance Levels

The XForms specification is intended for implementation on hardware platforms of all sizes, from tiny hand-held devices to high-powered servers. For this reason, a separate document is being developed to describe a conformance profile of XForms that can be processed with fewer resources.

12.1.1 XForms Full

This conformance level is suitable for more powerful forms processing, such as might be found on a standard desktop browser or a distributed XForms Processor involving server-side components. XForms Full implementations must return "full" from the property method (defined at 7.9.1 The property() Function ) called with the "conformance-level" parameter string.

12.2 Conformance Description

12.2.1 Conforming XForms Processors

All XForms Processors must conform to the following specifications, except as qualified below:

[XML 1.0]
[XML Names]
[XML Events]
[XPath 1.0] Implementing all features.
[XML Schema part 2]

All XForms Processors must fully support the following XForms modules: Core; MustUnderstand; Form Controls; Group; Switch; Repeat; and Action.

All XForms Processors must also support: the XForms Processing Model and all events listed at 4 Processing Model; the http scheme for processing xsd:anyURI; all serialization methods defined at 11 Submit.

A host language may introduce additional conformance requirements.

XForms Full Processors must implement all required features defined in this specification.

12.2.2 Conforming XForms Documents

All XForms Containing Documents must conform to the following specifications, except as qualified below:

[XML 1.0]
[XML Names]
[XML Events]
[XML Schema part 2]

XForms elements are typically inserted into a containing document in multiple places. The root element for each individual fragment must be model, a form control, group, repeat, or switch. Individual XForms fragments must be schema-valid against the Schema for XForms (A Schema for XForms).

A host language may introduce additional conformance requirements.

All XForms Full conforming documents must conform to all required portions of this specification.

12.2.3 Conforming XForms Generators

XForms generators must generate conforming XForms documents.

13 Glossary Of Terms

Binding: [Definition: A "binding" connects an instance data node to a form control or to a model item constraint by using a binding expression as a locater.]
Binding expression: [Definition: An [XPath 1.0] expression used in a binding.]
Computed expression: [Definition: An [XPath 1.0] expression used by model item properties such as relevant and calculate to include dynamic functionality in XForms.]
Containing document: [Definition: A specific document, for example an XHTML document, in which one or more <model> elements are found.]
Datatype: [Definition: From XML Schema [XML Schema part 2]: A 3-tuple, consisting of a) a set of distinct values, called its value space, b) a set of lexical representations, called its lexical space, and c) a set of facets that characterize properties of the value space, individual values or lexical items.]
Facet: [Definition: From XML Schema [XML Schema part 2]: A single defining aspect of a value space. Generally speaking, each facet characterizes a value space along independent axes or dimensions.]
First node rule: [Definition: When a UI Single-Node Binding attribute selects a node-set of size > 1, the first node in the node-set is used.]
Form control: [Definition: An XForms user interface control that serves as a point of user interaction.]
Host language: [Definition: An XML vocabulary, such as XHTML, into which XForms is embedded.]
Instance data: [Definition: An internal tree representation of the values and state of all the instance data nodes associated with a particular form.]
Instance data node: [Definition: An [XPath 1.0] node from the instance data.]
Lexical space: [Definition: From XML Schema [XML Schema part 2]: A lexical space is the set of valid literals for a datatype.]
Model Binding expression: [Definition: An [XPath 1.0] expression used in a binding that declares a model item property.]
Model item: [Definition: An instance data node with associated constraints.]
Model item property: [Definition: An XForms-specific annotation to an instance data node.]
QNameButNotNCNAME: [Definition: A QName that is not an NCName. In 2006, the W3C named this a PrefixedName. ]
Schema constraint: [Definition: A restriction, applied to form data, based on XML Schema datatypes.]
UI or Action Binding expression: [Definition: An [XPath 1.0] expression used in binding a form control to the instance, or to specify the node or node-set for operation by an action.]
Value space: [Definition: From XML Schema [XML Schema part 2]: A set of values for a given datatype. Each value in the value space of a datatype is denoted by one or more literals in its lexical space.]
versionList: [Definition: A list ([XML Schema part 2]) with an atomic datatype ([XML Schema part 2]) of versionNumber.]
versionNumber: [Definition: A string consisting of a non-zero digit (1 to 9) followed by zero or more digits (0 to 9), then a period character (.), and then one or more digits (0-9). A version number is derived from string by restriction based on the following pattern value (excluding the quote marks): "[1-9]\d*\.\d+".]
XForms Model: [Definition: The non-visible definition of an XML form as specified by XForms. The XForms Model defines the individual model items and constraints and other run-time aspects of XForms.]
XForms Processor: [Definition: A software application or program that implements and conforms to the XForms specification.]

Input Mode Token	Comments
arabic	Unicode script name
armenian	Unicode script name
bengali	Unicode script name
bopomofo	Unicode script name
braille	used to input braille patterns (not to indicate a braille input device)
buhid	Unicode script name
canadianAboriginal	Unicode script name
cherokee	Unicode script name
cyrillic	Unicode script name
deseret	Unicode script name
devanagari	Unicode script name
ethiopic	Unicode script name
georgian	Unicode script name
greek	Unicode script name
gothic	Unicode script name
gujarati	Unicode script name
gurmukhi	Unicode script name
han	Unicode script name
hangul	Unicode script name
hanja	Subset of 'han' used in writing Korean
hanunoo	Unicode script name
hebrew	Unicode script name
hiragana	Unicode script name (may include other Japanese scripts produced by conversion from hiragana)
ipa	International Phonetic Alphabet
kanji	Subset of 'han' used in writing Japanese
kannada	Unicode script name
katakana	Unicode script name (full-width, not half-width)
khmer	Unicode script name
lao	Unicode script name
latin	Unicode script name
malayalam	Unicode script name
math	mathematical symbols and related characters
mongolian	Unicode script name
myanmar	Unicode script name
ogham	Unicode script name
oldItalic	Unicode script name
oriya	Unicode script name
runic	Unicode script name
simplifiedHanzi	Subset of 'han' used in writing Simplified Chinese
sinhala	Unicode script name
syriac	Unicode script name
tagalog	Unicode script name
tagbanwa	Unicode script name
tamil	Unicode script name
telugu	Unicode script name
thaana	Unicode script name
thai	Unicode script name
tibetan	Unicode script name
traditionalHanzi	Subset of 'han' used in writing Traditional Chinese
user	Special value denoting the 'native' input of the user (e.g. to input her name or text in her native language).
yi	Unicode script name

Input Mode Token	Comments
lowerCase	lowercase (for bicameral scripts)
upperCase	uppercase (for bicameral scripts)
titleCase	title case (for bicameral scripts): words start with an upper case letter
startUpper	start input with one uppercase letter, then continue with lowercase letters
digits	digits of a particular script (e.g. inputmode='thai digits')
symbols	symbols, punctuation (suitable for a particular script)
predictOn	text prediction switched on (e.g. for running text)
predictOff	text prediction switched off (e.g. for passwords)
halfWidth	half-width compatibility forms (e.g. Katakana; deprecated)

Caption:	`inputmode`
Family name	hiragana
(in kana)	katakana
Given name	hiragana
(in kana)	katakana
Zip code	latin digits
Address	hiragana
(in kana)	katakana
Email	latin lowerCase
Telephone	latin digits
Comments	user predictOn

Name	Defined in:	Relationship to XForms
`:enabled` & `:disabled`	[CSS3]	Selects any form control bound to a node with the model item property `relevant` evaluating to true or false (respectively).
`:required` & `:optional`	TBD	Selects any form control bound to a node with the model item property `required` evaluating to true or false (respectively).
`:valid` & `:invalid`	TBD	Selects any form control bound to a node that is currently valid or invalid (respectively), as defined by XForms 1.0.
`:read-only` & `:read-write`	TBD	Selects any form control bound to a node with the model item property `readonly` evaluating to true or false (respectively).
`:out-of-range` & `:in-range`	TBD	Selects any form control bound to a node that contains a value the form control is not or is capable of rendering, (respectively).

Name	Defined in:	Relationship to XForms
`::value`	TBD	Represents the "active" area of a form control excluding the label; this corresponds in HTML to `input` and other form control elements. This pseudo-element is a child of the form control element, and appears immediately after the required `label` element.
`::repeat-item`	TBD	Represents a single item from a repeating sequence. Its position is as a parent to all the elements in a single repeating item. Each `::repeat-item` is associated with a particular instance data node, and is affected by the model item properties (e.g. '`relevant`') found there, as the related style properties will cascade to the child elements.
`::repeat-index`	TBD	Represents the current item of a repeating sequence. Its position is as a parent of all the elements in the index repeating item (and as a child to the `::repeat-item` pseudo-element), thus any style declarations applying to this pseudo-element override those on the parent `::repeat-item`.

XForms 1.0 (Third Edition)

W3C Recommendation 29 October 2007

Abstract

Status of this Document

Table of Contents

Appendices

1 About the XForms 1.0 Specification

1.1 Background

1.2 Reading the Specification

1.3 How the Specification is Organized

1.4 Documentation Conventions

2 Introduction to XForms

2.1 An Example

2.2 Providing XML Instance Data

2.3 Constraining Values

2.4 Multiple Forms per Document

3 Document Structure

3.1 The XForms Namespace

3.2 XForms Core Attribute Collections

3.2.1 Common Attributes

3.2.2 Linking Attributes

3.2.3 Single-Node Binding Attributes

3.2.4 Node-Set Binding Attributes

3.2.5 Model Item Property Attributes

3.3 The XForms Core Module

3.3.1 The model Element

3.3.2 The instance Element

3.3.3 The submission Element

3.3.4 The bind Element

3.4 The XForms MustUnderstand Module

3.5 The XForms Extension Module

3.5.1 The extension Element

4 Processing Model

4.1 Events Overview

4.2 Initialization Events

4.2.1 The xforms-model-construct Event

4.2.2 The xforms-model-construct-done Event

4.2.3 The xforms-ready Event

4.2.4 The xforms-model-destruct Event

4.3 Interaction Events

4.3.1 The xforms-next and xforms-previous Events

4.3.2 The xforms-focus Event

4.3.3 The xforms-help and xforms-hint Events

4.3.4 The xforms-refresh Event

4.3.5 The xforms-revalidate Event

4.3.6 The xforms-recalculate Event

4.3.7 The xforms-rebuild Event

4.3.8 The xforms-reset Event

4.3.9 The xforms-submit Event

4.4 Notification Events

4.4.1 The DOMActivate Event

4.4.2 The xforms-value-changed Event

4.4.3 The xforms-select and xforms-deselect Events

4.4.4 The xforms-scroll-first and xforms-scroll-last Events

4.4.5 The xforms-insert and xforms-delete Events

4.4.6 The xforms-valid Event

4.4.7 The xforms-invalid Event

4.4.8 The DOMFocusIn Event

4.4.9 The DOMFocusOut Event

4.4.10 The xforms-readonly Event

4.4.11 The xforms-readwrite Event

4.4.12 The xforms-required Event

4.4.13 The xforms-optional Event

4.4.14 The xforms-enabled Event

4.4.15 The xforms-disabled Event

4.4.16 The xforms-in-range Event

4.4.17 The xforms-out-of-range Event

4.4.18 The xforms-submit-done Event

4.4.19 The xforms-submit-error Event

4.5 Error Indications

4.5.1 The xforms-binding-exception Event

4.5.2 The xforms-link-exception Event

4.5.3 The xforms-link-error Event

4.5.4 The xforms-compute-exception Event

4.5.5 The xforms-version-exception Event

4.6 Event Sequencing

4.6.1 For input, secret, textarea, range, or upload Controls

4.6.2 For output Controls

4.6.3 For select or select1 Controls

4.6.4 For trigger Controls

4.6.1 For `input`, `secret`, `textarea`, `range`, or `upload` Controls

4.6.2 For `output` Controls

4.6.3 For `select` or `select1` Controls

4.6.4 For `trigger` Controls

4.6.5 For `submit` Controls

7.9.1 `The property() Function`