<pre class='metadata'>

Title: Media Queries Level 4

Group: csswg

Shortname: mediaqueries

Level: 4

Status: ED

Status Text: There is currently no preliminary interoperability or implementation report.

Work Status: refining

Implementation Report: https://wpt.fyi/results/css/mediaqueries

ED: https://drafts.csswg.org/mediaqueries-4/

TR: https://www.w3.org/TR/mediaqueries-4/

Previous Version: https://www.w3.org/TR/2021/CRD-mediaqueries-4-20211225/

Editor: Florian Rivoal, Invited Expert, https://florian.rivoal.net, w3cid 43241

Editor: Tab Atkins Jr., Google, http://xanthir.com/contact/, w3cid 42199

Former Editor: Håkon Wium Lie, Opera, howcome@opera.com

Former Editor: Tantek Çelik, Mozilla, tantek@cs.standard.edu

Former Editor: Daniel Glazman, Disruptive Innovations, daniel@glazman.org

Former Editor: Anne van Kesteren, Mozilla, annevk@annevk.nl

Abstract: <a>Media Queries</a> allow authors to test and query values or features of the user agent or display device, independent of the document being rendered. They are used in the CSS @media rule to conditionally apply styles to a document, and in various other contexts and languages, such as HTML and JavaScript.

Abstract:

Abstract: Media Queries Level 4 describes the mechanism and syntax of media queries, media types, and media features. It extends and supersedes the features defined in Media Queries Level 3.

Ignored Terms: min-resolution, max-resolution, none, view-mode, mediaText, CSSOMString

Link Defaults: css-break-3 (property) break-inside

Can I Use URL: https://drafts.csswg.org/mediaqueries-4/

Can I Use URL: http://drafts.csswg.org/mediaqueries-4/

Can I Use URL: https://drafts.csswg.org/mediaqueries/

Can I Use URL: http://drafts.csswg.org/mediaqueries/

Can I Use URL: https://www.w3.org/TR/mediaqueries-4/

Can I Use URL: http://www.w3.org/TR/mediaqueries-4/

Ignore Can I Use URL Failure: https://drafts.csswg.org/mediaqueries-4/

Ignore Can I Use URL Failure: http://drafts.csswg.org/mediaqueries-4/

Ignore Can I Use URL Failure: https://drafts.csswg.org/mediaqueries/

Ignore Can I Use URL Failure: http://drafts.csswg.org/mediaqueries/

Ignore Can I Use URL Failure: http://www.w3.org/TR/mediaqueries-4/

</pre>

<pre class=link-defaults>

spec:css-values-3; type:value; text:in

spec:css-values-3; type:value; text:cm

spec:css-values-3; type:value; text:px

spec:css-values-3; type:value; text:em

spec:css-values-3; type:type; text:<dimension>

spec:css-values-3; type:type; text:<ident>

spec:css-values-3; type:grammar; text:|

spec:css-values-3; type:grammar; text:?

spec:css-conditional-3; type:at-rule; text:@media

</pre>

<pre class=biblio>

{

"ITU-R-BT-2020-2": {

"href": "https://www.itu.int/rec/R-REC-BT.2020/en",

"title": "Parameter values for ultra-high definition television systems for production and international programme exchange",

"date": "October 2015"

},

"Display-P3": {

"title": "Display P3",

"authors": "Apple, Inc",

"date": "2022-02",

"href": "https://www.color.org/chardata/rgb/DisplayP3.xalter"

}

}

</pre>

<h2 id="intro">

Introduction</h2>

<em>This section is not normative.</em>

In 1997, HTML4 [[HTML401]] defined a mechanism to support media-dependent style sheets,

tailored for different <a>media types</a>.

For example, a document may use different style sheets for screen and for print.

In HTML, this can be written as:

<div class="example">

<pre>

&lt;link rel="stylesheet" type="text/css" media="screen" href="style.css">

&lt;link rel="stylesheet" type="text/css" media="print" href="print.css">

</pre>

</div>

CSS adapted and extended this functionality with its ''@media'' and ''@import'' rules,

adding the ability to query the value of individual features:

<div class="example">

Inside a CSS style sheet,

one can declare that sections apply to certain <a>media types</a>:

<pre>

@media screen {

* { font-family: sans-serif }

}

</pre>

Similarly, stylesheets can be conditionally imported based on media queries:

<pre>@import "print-styles.css" print;</pre>

</div>

<a>Media queries</a> can be used with HTML, XHTML, XML [[xml-stylesheet]] and the @import and @media rules of CSS.

<div class="example">

Here is the same example written in HTML, XHTML, XML, @import and @media:

<pre>

&lt;link media="screen and (color), projection and (color)"

rel="stylesheet" href="example.css">

&lt;link media="screen and (color), projection and (color)"

rel="stylesheet" href="example.css" />

&lt;?xml-stylesheet media="screen and (color), projection and (color)"

rel="stylesheet" href="example.css" ?>

@import url(example.css) screen and (color), projection and (color);

@media screen and (color), projection and (color) { … }

</pre>

</div>

<h3 id="placement">

Module interactions</h3>

This module replaces and extends the Media Queries, Media Type and Media Features

defined in [[!CSS2]] sections 7 and in [[!MEDIAQUERIES-3]].

<h3 id="values">

Values</h3>

Value types not defined in this specification, such as <<integer>>,

<<number>> or <<resolution>>, are defined in [[!CSS-VALUES-3]]. Other CSS

modules may expand the definitions of these value types.

<h3 id="units">

Units</h3>

The units used in media queries are the same as in other parts of CSS, as

defined in [[!CSS-VALUES-3]]. For example, the pixel unit represents CSS pixels and

not physical pixels.

<a spec="css-values-3">Relative length</a> units in media queries are based on the <a>initial value</a>, which means

that units are never based on results of declarations. <span class=note>For example, in HTML,

the ''em'' unit is relative to the <a>initial value</a> of 'font-size',

defined by the user agent or the user's preferences,

not any styling on the page.</span>

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<h2 id="media">

Media Queries</h2>

A <dfn export>media query</dfn> is a method of testing certain aspects of the user agent

or device that the document is being displayed in.

<a>Media queries</a> are (almost) always independent of the contents of the document,

its styling,

or any other internal aspect;

they're only dependent on “external” information

unless another feature explicitly specifies that it affects the resolution of Media Queries.

The syntax of a <a>media query</a> consists of

an optional <a>media query modifier</a>,

an optional <a>media type</a>,

and zero or more <a>media features</a>:

<pre class='railroad'>

Or:

N: media condition

And:

Or: 1

T: only

S:

T: not

N: media type

Opt:

And:

T: and

N: media condition

</pre>

A <a>media query</a> is a logical expression that is either true or false.

A media query is true if:

* the <a>media type</a>,

if specified,

matches the media type of the device where the user agent is running, and

* the <a>media condition</a> is true.

Statements regarding media queries in this section assume the <a href="#mq-syntax">syntax section</a> is followed.

Media queries that do not conform to the syntax are discussed in [[#error-handling]].

I.e. the syntax takes precedence over requirements in this section.

<div class="example">

Here is a simple example written in HTML:

<pre>&lt;link rel="stylesheet" media="screen and (color)" href="example.css" /></pre>

This example expresses that a certain style sheet

(<code>example.css</code>) applies to devices of a certain media type

(''screen'') with certain feature (it must be a color screen).

Here is the same media query written in an @import-rule in CSS:

<pre>@import url(example.css) screen and (color);</pre>

</div>

User agents must re-evaluate <a>media queries</a> in response to changes in the user environment that they're aware of,

for example if the device is tiled from landscape to portrait orientation,

and change the behavior of any constructs dependent on those <a>media queries</a> accordingly.

Unless another feature explicitly specifies that it affects the resolution of Media Queries, it is never necessary to apply a style sheet in order to evaluate expressions.

<h3 id='mq-list'>

Combining Media Queries</h3>

Several <a>media queries</a> can be combined into a comma-separated <dfn export>media query list</dfn>.

<pre class='railroad'>

Star:

N: media query

T: ,

</pre>

A <a>media query list</a> is true if <em>any</em> of its component <a>media queries</a> are true,

and false only if <em>all</em> of its component <a>media queries</a> are false.

<div class="example">

For example, the following <a>media query list</a> is true if either

the <a>media type</a> is ''screen'' and it's a color device,

<strong>or</strong> the <a>media type</a> is ''projection'' and it's a color device:

<pre>

@media screen and (color), projection and (color) { … }

</pre>

</div>

An empty <a>media query list</a> evaluates to true.

<div class="example">

For example, these are equivalent:

<pre>

@media all { … }

@media { … }

</pre>

</div>

<h3 id='mq-prefix'>

Media Query Modifiers</h3>

A <a>media query</a> may optionally be prefixed by a single <dfn export>media query modifier</dfn>,

which is a single keyword which alters the meaning of the following <a>media query</a>.

<h4 id='mq-not'>

Negating a Media Query: the ''not'' keyword</h4>

An individual <a>media query</a> can have its result negated

by prefixing it with the keyword <dfn value for="@media">not</dfn>.

If the <a>media query</a> would normally evaluate to true,

prefixing it with ''not'' makes it evaluate to false,

and vice versa.

<div class="example">

For example, the following will apply to everything except color-capable screens.

Note that the entire media query is negated,

not just the <a>media type</a>.

<pre>&lt;link rel="stylesheet" media="not screen and (color)" href="example.css" /></pre>

</div>

<h4 id='mq-only'>

Hiding a Media Query From Legacy user agents: the ''only'' keyword</h4>

The concept of <a>media queries</a> originates from HTML4 [[HTML401]].

That specification only defined <a>media types</a>,

but had a forward-compatible syntax that accommodated the addition of future concepts like <a>media features</a>:

it would consume the characters of a <a>media query</a> up to the first non-alphanumeric character,

and interpret that as a <a>media type</a>,

ignoring the rest.

For example, the <a>media query</a> ''screen and (color)''

would be truncated to just ''screen''.

Unfortunately, this means that legacy user agents using this error-handling behavior

will ignore any <a>media features</a> in a <a>media query</a>,

even if they're far more important than the <a>media type</a> in the query.

This can result in styles accidentally being applied in inappropriate situations.

To hide these <a>media queries</a> from legacy user agents,

the <a>media query</a> can be prefixed with the keyword <dfn value for="@media">only</dfn>.

The ''only'' keyword <strong>has no effect</strong> on the <a>media query</a>’s result,

but will cause the <a>media query</a> to be parsed by legacy user agents

as specifying the unknown <a>media type</a> “only”,

and thus be ignored.

<div class="example">

In this example, the stylesheet specified by the <code>&lt;link></code> element

will not be used by legacy user agents,

even if they would normally match the ''screen'' <a>media type</a>.

<pre>&lt;link rel="stylesheet" media="only screen and (color)" href="example.css" /></pre>

</div>

Note: Note that the ''only'' keyword can only be used before a <a>media type</a>.

A <a>media query</a> consisting only of <a>media features</a>,

or one with another <a>media query modifier</a> like ''not'',

will be treated as false by legacy user agents automatically.

Note: At the time of publishing this specification,

such legacy user agents are extremely rare,

and so using the ''only'' modifier is rarely, if ever, necessary.

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<h3 id='media-types'>

Media Types</h3>

A <dfn export>media type</dfn> is a broad category of user-agent devices

on which a document may be displayed.

The original set of <a>media types</a> were defined in HTML4,

for the <code>media</code> attribute on <code>&lt;link></code> elements.

Unfortunately, <a>media types</a> have proven insufficient as a way of discriminating between devices with different styling needs.

Some categories which were originally quite distinct,

such as ''screen'' and ''handheld'',

have blended significantly in the years since their invention.

Others, such as ''tty'' or ''tv'',

expose useful differences from the norm of a full-featured computer monitor,

and so are potentially useful to target with different styling,

but the definition of <a>media types</a> as mutually exclusive

makes it difficult to use them in a reasonable manner;

instead, their exclusive aspects are better expressed as <a>media features</a>

such as '@media/grid' or 'scan'.

As such, the following <a>media types</a> are defined for use in <a>media queries</a>:

<dl dfn-type=value dfn-for="@media">

<dt><dfn>all</dfn>

<dd>Matches all devices.

<dt><dfn>print</dfn>

<dd>Matches printers, and devices intended to reproduce a printed display,

such as a web browser showing a document in “Print Preview”.

<dt><dfn>screen</dfn>

<dd>Matches all devices that aren't matched by ''print''.

</dl>

In addition, the following <strong>deprecated</strong> <a>media types</a> are defined.

Authors must not use these <a>media types</a>;

instead, it is recommended that they select appropriate <a>media features</a>

that better represent the aspect of the device that they are attempting to style against.

User agents must recognize the following <a>media types</a> as valid,

but must make them match nothing.

<ul dfn-type=value dfn-for="@media">

<li><dfn>tty</dfn>

<li><dfn>tv</dfn>

<li><dfn>projection</dfn>

<li><dfn>handheld</dfn>

<li><dfn>braille</dfn>

<li><dfn>embossed</dfn>

<li><dfn>aural</dfn>

<li><dfn>speech</dfn>

</ul>

Note: It is expected that all of the media types will also be deprecated in time,

as appropriate <a>media features</a> are defined which capture their important differences.

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<h3 id='mq-features'>

Media Features</h3>

A <dfn export>media feature</dfn> is a more fine-grained test than <a>media types</a>,

testing a single, specific feature of the user agent or display device.

Syntactically, <a>media features</a> resemble CSS properties:

they consist of a feature name, a colon, and a value to test for.

They may also be written in boolean form as just a feature name,

or in range form with a comparison operator.

<pre class='railroad'>

T: (

Choice:

And:

N: feature name

T: :

N: feature value

N: feature name

And:

N: range form

C: (see below)

T: )

</pre>

There are, however, several important differences between properties and media features:

<ul>

<li>

Properties are used to give information about how to present a document.

Media features are used to describe requirements of the output device.

<li>

Media features are always wrapped in parentheses

and combined with the ''and'' or ''or'' keywords,

like ''(color) and (min-width: 600px)'',

rather than being separated with semicolons.

<li>

A media feature may be given with <em>only</em> its name

(omitting the colon and value)

to evaluate the feature in a <a>boolean context</a>.

This is a convenient shorthand for features that have a reasonable value representing 0 or “none”.

For example, ''(color)'' is true if the '@media/color' <a>media feature</a> is non-zero.

<li>

<a>Media features</a> with “range” type can be written in a <a>range context</a>,

which uses standard mathematical comparison operators rather than a colon,

or have their feature names <a href=#mq-min-max>prefixed with “min-” or “max-”</a>.

<li>

Properties sometimes accept complex values,

e.g., calculations that involve several other values.

<a>Media features</a> only accept single values: one keyword, one number, etc.

</ul>

If a <a>media feature</a> references a concept which does not exist on the device where the UA is running

(for example, speech UAs do not have a concept of “width”),

the <a>media feature</a> must always evaluate to false.

<div class="example">

The media feature ''device-aspect-ratio'' only applies to

visual devices. On an ''speech'' device, expressions involving

''device-aspect-ratio'' will therefore always be false:

<pre>

&lt;link media="speech and (device-aspect-ratio: 16/9)"

rel="stylesheet" href="example.css">

</pre>

</div>

<h4 id='mq-ranges'>

Media Feature Types: “range” and “discrete”</h4>

Every media feature defines its “type” as either “range” or “discrete” in its definition table.

“Discrete” media features,

like 'pointer'

take their values from a set.

The values may be keywords

or boolean numbers (0 and 1),

but the common factor is that there's no intrinsic “order” to them--

none of the values are “less than” or “greater than” each other.

“Range” media features like '@media/width', on the other hand,

take their values from a range.

Any two values can be compared to see which is lesser and which is greater.

The only significant difference between the two types is that “range” <a>media features</a>

can be evaluated in a <a>range context</a>

and accept “min-” and “max-” prefixes on their name.

Doing either of these changes the meaning of the feature--

rather than the <a>media feature</a> being true when the feature exactly matches the given value,

it matches when the feature is greater than/less than/equal to the given value.

<div class='example'>

A ''(width >= 600px)'' <a>media feature</a> is true

when the viewport's width is ''600px'' <em>or more</em>.

On the other hand, ''(width: 600px)'' by itself is only true

when the viewport's width is <em>exactly</em> ''600px''.

If it's less or greater than ''600px'', it'll be false.

</div>

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<h4 id='mq-boolean-context'>

Evaluating Media Features in a Boolean Context</h4>

While <a>media features</a> normally have a syntax similar to CSS properties,

they can also be written more simply as just the feature name,

like ''(color)''.

When written like this, the <a>media feature</a> is evaluated in a <dfn export>boolean context</dfn>.

If the feature would be true for any value

<em>other than</em> the number ''0'',

a <<dimension>> with the value ''0'',

or the keyword ''@media/update/none'',

the <a>media feature</a> evaluates to true.

Otherwise, it evaluates to false.

<div class='example'>

Some <a>media features</a> are designed to be written like this.

For example, 'update' is typically written as ''(update)'' to test if any kind of updating is available,

or ''not (update)'' to check for the opposite.

It can still be given an explicit value as well,

with ''(update: fast) or (update: slow)'' equal to ''(update)'',

and ''(update: none)'' equal to ''not (update)''.

</div>

<div class='example'>

Some numeric <a>media features</a>, like '@media/width',

are rarely if ever useful to evaluate in a <a>boolean context</a>,

as their values are almost always greater than zero.

Others, like '@media/color', have meaningful zero values:

''(color)'' is identical to ''(color > 0)'',

indicating that the device is capable of displaying color at all.

</div>

<div class='example'>

Only some of the <a>media features</a> that accept keywords are meaningful in a <a>boolean context</a>.

For example, ''(pointer)'' is useful,

as 'pointer' has a ''pointer/none'' value to indicate there's no pointing device at all on the device.

Similarly, ''not (color-gamut)'' can be useful to detect a very low-quality screen,

as such a device won't match any of the '@media/color-gamut' keywords;

even tho '@media/color-gamut' lacks a <css>none</css> keyword,

it'll still be false in a [=boolean context=]

because none of its values match.

On the other hand, ''(scan)'' is just always true or always false

(depending on whether it applies at all to the device),

as, if it applies at all,

the device is guaranteed to match at least one of its values.

</div>

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<h4 id="mq-range-context">

Evaluating Media Features in a Range Context</h4>

<a>Media features</a> with a “range” type can be alternately written in a <dfn export>range context</dfn>

that takes advantage of the fact that their values are ordered,

using ordinary mathematical comparison operators:

<pre class='railroad'>

T: (

Choice:

Seq:

N: feature name/value

Choice: 4

T: =

T: <

T: <=

T: >

T: >=

N: feature value/name

Seq:

N: value

Choice:

T: <

T: <=

N: feature name

Choice:

T: <

T: <=

N: value

Seq:

N: value

Choice:

T: >

T: >=

N: feature name

Choice:

T: >

T: >=

N: value

T: )

</pre>

Note: This syntax is new to Level 4 of Mediaqueries,

and thus is not as widely supported at the moment

as the ''min-''/''max-'' prefixes.

The basic form,

consisting of a feature name,

a comparison operator,

and a value,

returns true if the relationship is true.

<div class='example'>

For example, ''(height > 600px)''

(or ''(600px &lt; height)'')

returns true if the viewport height is greater than ''600px''.

</div>

The remaining forms,

with the feature name nested between two value comparisons,

returns true if both comparisons are true.

<div class='example'>

For example, ''(400px &lt; width &lt; 1000px)'' returns true if the viewport width is between ''400px'' and ''1000px''

(but not equal to either).

</div>

Some media features with a "range" type are said to be <dfn>false in the negative range</dfn>.

This means that negative values are valid and must be parsed, and that

querying whether the media feature is equal to, less than, or less or equal than

any such negative value must evaluate to false.

Querying whether the media feature is greater, or greater or equal, than a negative

value evaluates to true if the relationship is true.

Note: If negative values had been rejected at parse time instead,

they would be treated as ''unknown'' based on the error handling rules.

However, in reality,

whether a device's '@media/resolution' is ''-300dpi'' is not unknown, it is known to be false.

Similarly, for any visual device, the '@media/width' of the targeted display area is known to be greater than ''-200px''

The above rule reflects that,

making intuition match what UAs do.

<div class=example>

The following examples result in a green background on all visual devices:

<pre><code class=lang-css>

@media not (width <= -100px) {

body { background: green; }

}

</code></pre>

<pre><code class=lang-css>

@media (height > -100px) {

body { background: green; }

}

</code></pre>

<pre><code class=lang-css>

@media not (resolution: -300dpi) {

body { background: green; }

}

</code></pre>

</div>

<div class=advisement>

This is a behavior change compared to Media Queries Level 3 [[MEDIAQUERIES-3]],

where negative values on these properties caused a syntax error.

In level 3, syntax errors—including forbidden values—resulted in the entire <a>media query</a> being false,

rather than the ''unknown'' treatment defined in this level.

Implementations updating from level 3 should make sure

to change the handling of negative values for the relevant properties

when they add support for the richer syntax defined in [[#media-conditions]],

to avoid introducing unintended semantics.

</div>

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<h4 id='mq-min-max'>

Using “min-” and “max-” Prefixes On Range Features</h4>

Rather than evaluating a “range” type <a>media feature</a> in a range context,

as described above,

the feature may be written as a normal <a>media feature</a>,

but with a “min-” or “max-” prefix on the feature name.

This is equivalent to evaluating the feature in a <a>range context</a>,

as follows:

<ul>

<li>

Using a “min-” prefix on a feature name is equivalent to using the “>=” operator.

For example, ''(min-height: 600px)'' is equivalent to ''(height >= 600px)''.

<li>

Using a “max-” prefix on a feature name is equivalent to using the “<=” operator.

For example, ''(max-width: 40em)'' is equivalent to ''(width <= 40em)''.

</ul>

Note: because “min-” and “max-” both equate to range comparisons that <strong>include</strong> the value,

they may be limiting in certain situations.

<div class='example'>

For instance,

authors trying to define different styles based on a breakpoint in the viewport width using “min-” and “max-”

would generally offset the values they're comparing,

to ensure that both queries don't evaluate to true simultaneously.

Assuming the breakpoint is at 320px, authors would conceptually use:

<pre>

@media (max-width: 320px) { /* styles for viewports <= 320px */ }

@media (min-width: 321px) { /* styles for viewports >= 321px */ }

</pre>

While this ensures that the two sets of styles don't apply simultaneously when the viewport width is 320px,

it does not take into account the possibility of fractional viewport sizes which can occur as a result of non-integer pixel densities

(e.g. on high-dpi displays or as a result of zooming/scaling).

Any viewport widths that fall between 320px and 321px will result in none of the styles being applied.

One approach to work around this problem is to increase the precision of the values used for the comparison. Using the example above,

changing the second comparison value to 320.01px significantly reduces the chance that a viewport width on a device would fall

between the cracks.

<pre>

@media (max-width: 320px) { /* styles for viewports <= 320px */ }

@media (min-width: 320.01px) { /* styles for viewports >= 320.01px */ }

</pre>

However, in these situations, <a>range context</a> queries (which are not limited to “>=” and “<=” comparisons) offer a more appropriate solution:

<pre>

@media (width <= 320px) { /* styles for viewports <= 320px */ }

@media (width > 320px) { /* styles for viewports > 320px */ }

</pre>

</div>

“Discrete” type properties do not accept “min-” or “max-” prefixes.

Adding such a prefix to a “discrete” type <a>media feature</a> simply results in an unknown feature name.

<div class='example'>

For example,

''(min-grid: 1)'' is invalid,

because '@media/grid' is a “discrete” <a>media feature</a>,

and so doesn't accept the prefixes.

(Even though the '@media/grid' <a>media feature</a> appears to be numeric,

as it accepts the values ''0'' and ''1''.)

</div>

Attempting to evaluate a min/max prefixed <a>media feature</a> in a <a>boolean context</a>

is invalid and a syntax error.

Combining Media Features {#media-conditions}

--------------------------------------------

Multiple <a>media features</a> can be combined together into a <dfn export>media condition</dfn>

using full boolean algebra

(not, and, or).

* Any media feature can be negated by placing ''not'' before it.

For example, ''not (color)'' inverts the meaning of ''(color)''--

since ''(color)'' matches a device with any kind of color display,

''not (color)'' matches a device <em>without</em> any kind of color display.

* Two or more media features can be chained together,

such that the query is only true if <em>all</em> of the media features are true,

by placing ''and'' between them.

For example, ''(width < 600px) and (height < 600px)''

only matches devices whose screens are smaller than ''600px'' wide in both dimensions.

* Alternately, two or more media features can be chained together,

such that the query is true if <em>any</em> of the media features are true,

by placing ''or'' between them.

For example, ''(update: slow) or (hover: none)''

matches if the device is slow to update the screen (such as an e-reader)

<em>or</em> the primary pointing device has no hover capability,

perhaps indicating that one should use a layout that displays more information

rather than compactly hiding it until the user hovers.

* <a>Media conditions</a> can be grouped by wrapping them in parentheses ''()''

which can then be nested within a condition the same as a single media query.

For example, ''(not (color)) or (hover)''

is true on devices that are monochrome

and/or that have hover capabilities.

If one instead wanted to query for a device that was monochrome and <em>didn't</em> have hover capabilities,

it must instead be written as ''not ((color) or (hover))''

(or, equivalently, as ''(not (color)) and (not (hover))'').

It is <em>invalid</em> to mix ''and'' and ''or'' and ''not'' at the same “level” of a media query.

For example, ''(color) and (pointer) or (hover)'' is illegal,

as it's unclear what was meant.

Instead, parentheses can be used to group things using a particular joining keyword,

yielding either ''(color) and ((pointer) or (hover))''

or ''((color) and (pointer)) or (hover)''.

These two have very different meanings:

if only ''(hover)'' is true,

the first one evaluates to false

but the second evaluates to true.

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<h2 id='mq-syntax'>

Syntax</h2>

Informal descriptions of the media query syntax appear in the prose and railroad diagrams in previous sections.

The formal media query syntax is described in this section,

with the rule/property grammar syntax defined in [[!CSS-SYNTAX-3]] and [[!CSS-VALUES-3]].

To parse a <dfn>&lt;media-query-list></dfn> production,

<a>parse a comma-separated list of component values</a>,

then parse each entry in the returned list as a <<media-query>>.

Its value is the list of <<media-query>>s so produced.

Note: This explicit definition of <<media-query-list>> parsing

is necessary to make the error-recovery behavior of <a>media query lists</a> well-defined.

Note: This definition of <<media-query-list>> parsing intentionally accepts an empty list.

Note: As per [[!CSS-SYNTAX-3]], tokens are <a>ASCII case-insensitive</a>.

<pre>

<dfn>&lt;media-query></dfn> = <<media-condition>>

| [ not | only ]? <<media-type>> [ and <<media-condition-without-or>> ]?

<dfn>&lt;media-type></dfn> = <<ident>>

<dfn>&lt;media-condition></dfn> = <<media-not>> | <<media-in-parens>> [ <<media-and>>* | <<media-or>>* ]

<dfn>&lt;media-condition-without-or></dfn> = <<media-not>> | <<media-in-parens>> <<media-and>>*

<dfn>&lt;media-not></dfn> = not <<media-in-parens>>

<dfn>&lt;media-and></dfn> = and <<media-in-parens>>

<dfn>&lt;media-or></dfn> = or <<media-in-parens>>

<dfn>&lt;media-in-parens></dfn> = ( <<media-condition>> ) | ( <<media-feature>> ) | <<general-enclosed>>

<dfn>&lt;media-feature></dfn> = [ <<mf-plain>> | <<mf-boolean>> | <<mf-range>> ]

<dfn>&lt;mf-plain></dfn> = <<mf-name>> : <<mf-value>>

<dfn>&lt;mf-boolean></dfn> = <<mf-name>>

<dfn>&lt;mf-range></dfn> = <<mf-name>> <<mf-comparison>> <<mf-value>>

| <<mf-value>> <<mf-comparison>> <<mf-name>>

| <<mf-value>> <<mf-lt>> <<mf-name>> <<mf-lt>> <<mf-value>>

| <<mf-value>> <<mf-gt>> <<mf-name>> <<mf-gt>> <<mf-value>>

<dfn>&lt;mf-name></dfn> = <<ident>>

<dfn>&lt;mf-value></dfn> = <<number>> | <<dimension>> | <<ident>> | <<ratio>>

<dfn>&lt;mf-lt></dfn> = '<' '='?

<dfn>&lt;mf-gt></dfn> = '>' '='?

<dfn>&lt;mf-eq></dfn> = '='

<dfn>&lt;mf-comparison></dfn> = <<mf-lt>> | <<mf-gt>> | <<mf-eq>>

<dfn>&lt;general-enclosed></dfn> = [ <<function-token>> <<any-value>>? ) ] | [ ( <<any-value>>? ) ]

</pre>

The <<media-type>> production does not include the keywords ''only'', ''not'', ''and'', ''or'', and ''layer''.

Note: The exclusion of ''layer'' is because

it would otherwise be ambiguous

when when used in the <code highlight=css>@import url(…) layer;</code> syntax

for the sake of [=cascade layers=].

See [[CSS-CASCADE-5]].

No whitespace is allowed between the “<” or “>” <<delim-token>>s and the following “=” <<delim-token>>,

if it's present.

Note: Whitespace is required between a ''not'', ''and'', or ''or'' keyword

and the following ''('' character,

because without it that would instead parse as a <<function-token>>.

This is not made explicitly invalid because it's already covered by the above grammar.

It's fine to have whitespace between a '')'' and a following keyword,

however.

When parsing the <<media-in-parens>> production,

the <<general-enclosed>> branch must only be chosen if the input does not match either of the preceding branches.

<span class='note'><<general-enclosed>> exists to allow for future expansion of the grammar in a reasonably compatible way.</span>

Evaluating Media Queries {#evaluating}

--------------------------------------

Each of the major subexpression of <<media-condition>> or <<media-condition-without-or>> is associated with a boolean result, as follows:

<dl>

<dt><<media-condition>>

<dt><<media-condition-without-or>>

<dd>

The result is the result of the child subexpression.

<dt><<media-in-parens>>

<dd>

The result is the result of the child term.

<dt><<media-not>>

<dd>

The result is the negation of the <<media-in-parens>> term.

The negation of unknown is unknown.

<dt><<media-in-parens>> <<media-and>>*

<dd>

The result is true if the <<media-in-parens>> child term

and all of the <<media-in-parens>> children of the <<media-and>> child terms are true,

false if at least one of these <<media-in-parens>> terms are false,

and unknown otherwise.

<dt><<media-in-parens>> <<media-or>>*

<dd>

The result is false if the <<media-in-parens>> child term

and all of the <<media-in-parens>> children of the <<media-or>> child terms are false,

true if at least one of these <<media-in-parens>> terms are true,

and unknown otherwise.

<dt><<general-enclosed>>

<dd>

The result is unknown.

Authors must not use <<general-enclosed>> in their stylesheets.

<span class='note'>It exists only for future-compatibility,

so that new syntax additions do not invalidate too much of a <<media-condition>> in older user agents.</span>

<dt><<media-feature>>

<dd>

The result is the result of evaluating the specified media feature.

</dl>

If the result of any of the above productions

is used in any context that expects a two-valued boolean,

“unknown” must be converted to “false”.

Note: This means that,

for example,

when a <a>media query</a> is used in a ''@media'' rule,

if it resolves to “unknown” it's treated as “false”

and fails to match.

<div class="note">

Media Queries use a three-value logic where terms can be “true”, “false”, or “unknown”.

Specifically, it uses the <a href="http://en.wikipedia.org/wiki/Three-valued_logic#Kleene_and_Priest_logics">Kleene 3-valued logic</a>.

In this logic, “unknown” means “either true or false, but we're not sure which yet”.

In general, an unknown value showing up in a formula will cause the formula to be unknown as well,

as substituting “true” for the unknown will give the formula a different result than substituting “false”.

The only way to eliminate an unknown value is to use it in a formula that will give the same result

whether the unknown is replaced with a true or false value.

This occurs when you have “false AND unknown” (evaluates to false regardless)

and “true OR unknown” (evaluates to true regardless).

This logic was adopted because <<general-enclosed>> needs to be assigned a truth value.

In standard boolean logic, the only reasonable value is “false”,

but this means that ''not unknown(function)'' is true,

which can be confusing and unwanted.

Kleene's 3-valued logic ensures that unknown things will prevent a <a>media query</a> from matching,

unless their value is irrelevant to the final result.

</div>

<h3 id="error-handling">

Error Handling</h3>

A media query that does not match the grammar in the previous section must be replaced by ''not all'' during parsing.

Note: Note that a grammar mismatch does <strong>not</strong> wipe out an entire <a>media query list</a>,

just the problematic <a>media query</a>.

The parsing behavior defined above automatically recovers at the next top-level comma.

<div class='example'>

<pre>

@media (example, all,), speech { /* only applicable to speech devices */ }

@media &test, speech { /* only applicable to speech devices */ }

</pre>

Both of the above <a>media query lists</a> are turned into ''not all, speech'' during parsing,

which has the same truth value as just ''speech''.

Note that error-recovery only happens at the top-level of a <a>media query</a>;

anything inside of an invalid parenthesized block

will just get turned into ''not all'' as a group.

For example:

<pre>

@media (example, speech { /* rules for speech devices */ }