Media query expected ошибка

Abstract

HTML4 and CSS2 currently support media-dependent style sheets tailored
for different media types. For example, a document may use
sans-serif fonts when displayed on a screen and serif fonts when printed.
‘screen’ and ‘print’ are two media types that have been defined.
Media queries extend the functionality of media types by allowing
more precise labeling of style sheets.

A media query consists of a media type and zero or more expressions that
check for the conditions of particular media features. Among the
media features that can be used in media queries are ‘width’, ‘height’, and ‘color’. By using media queries, presentations can
be tailored to a specific range of output devices without changing the
content itself.

Status of this Document

This section describes the status of this document at the time of its publication. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This document was published by the
CSS Working Group
as a Recommendation using the
Recommendation track.
It includes proposed corrections.

A W3C Recommendation is a specification that, after extensive consensus-building, is endorsed by W3C and its Members, and has commitments from Working Group members to royalty-free licensing for implementations.

W3C recommends the wide deployment of this specification as a standard for the Web.

Please send feedback
by filing issues in GitHub (preferred),
including the spec code “mediaqueries-3” in the title, like this:
“[mediaqueries-3] …summary of comment…”.
All issues and comments are archived.
Alternately, feedback can be sent to the (archived) public mailing list www-style@w3.org.
Comments are due by 5 June 2022.

This document is governed by the 2 November 2021 W3C Process Document.

This document was produced by a group operating under the W3C Patent Policy.
W3C maintains a public list of any patent disclosures made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains Essential
Claim(s) must disclose the information in accordance with section 6 of the
W3C Patent Policy.

1. Background

(This section is not normative.)

HTML4 [HTML401]
and CSS2 [CSS21]
currently support media-dependent style sheets tailored for different
media types. For example, a document may use different style sheets for
screen and print. In HTML4, this can be written as:

<link rel="stylesheet" type="text/css" media="screen" href="sans-serif.css">
<link rel="stylesheet" type="text/css" media="print" href="serif.css">

Inside a CSS style sheet, one can declare that sections apply to certain
media types:

@media screen {
  * { font-family: sans-serif }
}

The ‘print’ and ‘screen’ media types are defined in HTML4. The
complete list of media types in HTML4 is: ‘aural’, ‘braille’, ‘handheld’, ‘print’, ‘projection’, ‘screen’, ‘tty’,
‘tv’. CSS2 defines the same list,
deprecates ‘aural’ and adds
‘embossed’ and ‘speech’. Also, ‘all’ is used to indicate that the style sheet
applies to all media types.

Media-specific style sheets are supported by several user agents. The
most commonly used feature is to distinguish between ‘screen’ and ‘print’.

There have been requests for ways to describe in more detail what type
of output devices a style sheet applies to. Fortunately HTML4 foresaw
these requests and defined a forward-compatible syntax for media types.
Here is a quote from HTML4,
section 6.13:

Future versions of HTML may introduce new values and may allow
parameterized values. To facilitate the introduction of these extensions,
conforming user agents must be able to parse the media
attribute value as follows:

1. The value is a comma-separated list of entries. For example,

   media="screen, 3d-glasses, print and resolution > 90dpi"

   is mapped to:

   "screen"
   "3d-glasses"
   "print and resolution > 90dpi"

2. Each entry is truncated just before the first character that isn’t a
   US ASCII letter [a-zA-Z] (Unicode decimal 65-90, 97-122), digit [0-9]
   (Unicode hex 30-39), or hyphen (45). In the example, this gives:

   "screen"
   "3d-glasses"
   "print"

Media queries, as described in this specification, build on the
mechanism outlined in HTML4. The syntax of media queries fit into the
media type syntax reserved in HTML4. The media
attribute of HTML4 also exists in XHTML and generic XML. The same syntax
can also be used inside in the ‘@media’
and ‘@import’ rules of CSS.

However, the parsing rules for media queries are incompatible with those
of HTML4 so that they are consistent with those of media queries used in
CSS.

Newer versions of HTML [HTML]
reference the Media Queries specification
directly and thus updates the rules for HTML.

A media query consists of a media type and zero or more expressions that check for the
conditions of particular media
features.

Statements regarding media queries in this section assume the syntax section is followed. Media queries that do not
conform to the syntax are discussed in the error
handling section. I.e. the syntax takes precedence over requirements
in this section.

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

@import url(color.css) screen and (color);

A media query is a logical expression that is either true or false. A
media query is true if the media type of the media query matches the media
type of the device where the user agent is running (as defined in the
«Applies to» line), and all expressions in the media query are true.

A shorthand syntax is offered for media queries that apply to all media
types; the keyword ‘all’ can be left
out (along with the trailing ‘and’).
I.e. if the media type is not explicitly given it is ‘all’.

@media all and (min-width:500px) { … }
@media (min-width:500px) { … }

@media (orientation: portrait) { … }
@media all and (orientation: portrait) { … }

Several media queries can be combined in a media query list. A
comma-separated list of media queries. If one or more of the media queries
in the comma-separated list are true, the whole list is true, and
otherwise false. In the media queries syntax, the comma expresses a
logical OR, while the ‘and’ keyword
expresses a logical AND.

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

If the media query list is empty (i.e. the declaration is the empty
string or consists solely of whitespace) it evaluates to true.

@media all { … }
@media { … }

The logical NOT can be expressed through the ‘not’ keyword. The presence of the keyword
‘not’ at the beginning of the media
query negates the result. I.e., if the media query had been true without
the ‘not’ keyword it will become false,
and vice versa. User agents that only support media types (as described in
HTML4) will not recognize the ‘not’
keyword and the associated style sheet is therefore not applied.

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

The keyword ‘only’ can also be used
to hide style sheets from older user agents. User agents must process
media queries starting with ‘only’ as
if the ‘only’ keyword was not present.

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

The media queries syntax can be used with HTML, XHTML, XML [XMLSTYLE] and the
@import and @media rules of CSS.

<link media="screen and (color), projection and (color)" rel="stylesheet" href="example.css">

<link media="screen and (color), projection and (color)" rel="stylesheet" href="example.css" />

<?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) { … }

If a media feature does not apply to the device where the UA is running,
expressions involving the media feature will be false.

<link rel="stylesheet" media="aural and (device-aspect-ratio: 16/9)" href="example.css" />

Expressions will always be false if the unit of measurement does not
apply to the device.

<link rel="stylesheet" media="speech and (min-device-width: 800px)" href="example.css" />

To avoid circular dependencies, unless another feature explicitly
specifies that it affects the resolution of Media Queries, it is not necessary to apply the style
sheet in order to evaluate expressions. For example, the aspect ratio of a
printed document may be influenced by a style sheet, but expressions
involving ‘device-aspect-ratio’ will be
based on the default aspect ratio of the user agent.

User agents are expected, but not required, to re-evaluate
and re-layout the page in response to changes in the user environment, for
example if the device is tilted from landscape to portrait mode.

3. Syntax

The media query syntax is described in terms of the CSS2 grammar. As such,
rules not defined here are defined in CSS2. The
media_query_list production defined below replaces the
media_list production from CSS2. [CSS21]

media_query_list
 : S* [media_query [ ',' S* media_query ]* ]?
 ;
media_query
 : [ONLY | NOT]? S* media_type S* [ AND S* expression ]*
 | expression [ AND S* expression ]*
 ;
media_type
 : IDENT
 ;
expression
 : '(' S* media_feature S* [ ':' S* expr ]? ')' S*
 ;
media_feature
 : IDENT
 ;

COMMENT tokens, as defined by CSS2, do not occur in the grammar (to keep
it readable), but any number of these tokens may appear anywhere between
other tokens. [CSS21]

The following new definitions are introduced:

L  l|\0{0,4}(4c|6c)(rn|[ trnf])?|\l
Y  y|\0{0,4}(59|79)(rn|[ trnf])?|\y

The following new tokens are introduced:

{O}{N}{L}{Y}      {return ONLY;}
{N}{O}{T}         {return NOT;}
{A}{N}{D}         {return AND;}
{num}{D}{P}{I}    {return RESOLUTION;}
{num}{D}{P}{C}{M} {return RESOLUTION;}

RESOLUTION is to be added to the CSS2 term
production.

CSS style sheets are generally ASCII
case-insensitive, and this is also the case for media queries.

In addition to conforming to the syntax, each media query needs to use
media types and media features according to their respective specification
in order to be considered conforming.

@media all { body { background:lime } }
@media example { body { background:red } }

3.1. Error Handling

For media queries that are not conforming user agents need to follow the
rules described in this section.

• Unknown media types. Unknown media types evaluate to
  false. Effectively, they are treated identically to known media types
  that do not match the media type of the device.
  However, an exception is made for media types ‘not’, ‘and’, ‘only’, and ‘or’.
  Even though they do match the IDENT production,
  they must not be treated as unknown media types,
  but rather trigger the malformed query clause.

  The media query «unknown» will evaluate to false, unless
  unknown is actually a supported media type. Similarly,
  «not unknown» will evaluate to true.

  The following is a malformed media query because it uses ‘only’ and ‘or’ as media types.

  @media only and or { … }

  Unknown media types are distinct from media types that do
  not actually match the IDENT production. Those fall under the malformed
  media query clause.

• Unknown media features. User agents are to represent
  a media query as «not all» when one of the specified media
  features is not known.

  <link rel="stylesheet" media="screen and (max-weight: 3kg) and (color), (color)" href="example.css" />

  In this example, the first media query will be represented as
  «not all» and evaluate to false and the second media query
  is evaluated as if the first had not been specified, effectively.

  @media (min-orientation:portrait) { … }

  Is represented as «not all» because the ‘orientation’ feature does not accept the
  ‘min-’ prefix.

• Unknown media feature values. As with unknown media
  features, user agents are to represent a media query as «not
all» when one of the specified media feature values is not known.

  The media query (color:20example) specifies an unknown
  value for the ‘color’ media feature
  and is therefore represented as «not all«.

  This media query is represented as «not all» because
  negative lengths are not allowed for the ‘width’ media feature:

  @media (min-width: -100px) { … }

• Malformed media query. User agents are to handle
  unexpected tokens encountered while parsing a media query by reading
  until the end of the media query, while observing the rules for
  matching pairs of (), [], {}, «», and », and correctly
  handling escapes. Media queries with unexpected tokens are represented
  as «not all«. [CSS21]

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

  The following is an malformed media query because having no space
  between ‘and’ and the expression is
  not allowed. (That is reserved for the functional notation syntax.)

  @media all and(color) { … }

  Media queries are expected to follow the error handling rules of the
  host language as well.

  @media test;,all { body { background:lime } }

  … will not apply because the semicolon terminates the
  @media rule in CSS.

Syntactically, media features resemble CSS properties: they have names
and accept certain values. There are, however, several important
differences between properties and media features:

• Properties are used in declarations to give information about
  how to present a document. Media features are used in
  expressions to describe requirements of the output device.

• Most media features accept optional ‘min-’ or ‘max-’
  prefixes to express «greater or equal to» and «smaller or equal to»
  constraints. This syntax is used to avoid «<» and «>» characters
  which may conflict with HTML and XML. Those media features that accept
  prefixes will most often be used with prefixes, but can also be used
  alone.

• Properties always require a value to form a declaration. Media
  features, on the other hand, can also be used without a value. For a
  media feature feature, (feature) will
  evaluate to true if (feature:x) will
  evaluate to true for a value x other than zero or zero
  followed by a unit identifier (i.e., other than 0,
  0px, 0em, etc.). Media features that are
  prefixed by min/max cannot be used without a value. When a media feature
  prefixed with min/max is used without a value it makes the media query
  malformed.

• Properties may accept more complex values, e.g., calculations that
  involve several other values. Media features only accept single values:
  one keyword, one number, or a number with a unit identifier. (The only
  exceptions are the ‘aspect-ratio’ and
  ‘device-aspect-ratio’ media features.)

For example, the ‘color’ media
feature can form expressions without a value (‘(color)’), or with a value (‘(min-color: 1)’).

This specification defines media features usable with visual
and tactile devices. Similarly, media features can be defined for aural
media types.

4.1. width

Value: <length>
Applies to: visual and tactile media types
Accepts min/max prefixes: yes

The ‘width’ media feature describes
the width of the targeted display area of the output device. For
continuous media, this is the width of the viewport (as described by CSS2,
section 9.1.1 [CSS21]) including the size of a
rendered scroll bar (if any). For paged media, this is the width of the
page box (as described by CSS2, section 13.2 [CSS21]).

A specified <length> cannot be negative.

<link rel="stylesheet" media="print and (min-width: 25cm)" href="http://…" />

@media screen and (min-width: 400px) and (max-width: 700px) { … }

@media handheld and (min-width: 20em),
  screen and (min-width: 20em) { … }

4.2. height

Value: <length>
Applies to: visual and tactile media types
Accepts min/max prefixes: yes

The ‘height’ media feature describes
the height of the targeted display area of the output device. For
continuous media, this is the height of the viewport including the size of
a rendered scroll bar (if any). For paged media, this is the height of the
page box.

A specified <length> cannot be negative.

4.3. device-width

Value: <length>
Applies to: visual and tactile media types
Accepts min/max prefixes: yes

The ‘device-width’ media feature
describes the width of the rendering surface of the output device. For
continuous media, this is the width of the screen. For paged media, this
is the width of the page sheet size.

A specified <length> cannot be negative.

@media screen and (device-width: 800px) { … }

4.4. device-height

Value: <length>
Applies to: visual and tactile media types
Accepts min/max prefixes: yes

The ‘device-height’ media feature
describes the height of the rendering surface of the output device. For
continuous media, this is the height of the screen. For paged media, this
is the height of the page sheet size.

A specified <length> cannot be negative.

<link rel="stylesheet" media="screen and (device-height: 600px)" />

4.5. orientation

Value: portrait |
landscape
Applies to: bitmap media types
Accepts min/max prefixes: no

The ‘orientation’ media feature is
‘portrait’ when the value of the
‘height’ media feature is greater than
or equal to the value of the ‘width’
media feature. Otherwise ‘orientation’
is ‘landscape’.

@media all and (orientation:portrait) { … }
@media all and (orientation:landscape) { … }

4.6. aspect-ratio

Value: <ratio>
Applies to: bitmap media types
Accepts min/max prefixes: yes

The ‘aspect-ratio’ media feature is
defined as the ratio of the value of the ‘width’ media feature to the value of the
‘height’ media feature.

4.7.
device-aspect-ratio

Value: <ratio>
Applies to: bitmap media types
Accepts min/max prefixes: yes

The ‘device-aspect-ratio’ media
feature is defined as the ratio of the value of the ‘device-width’ media feature to the value of the
‘device-height’ media feature.

@media screen and (device-aspect-ratio: 16/9) { … }
@media screen and (device-aspect-ratio: 32/18) { … }
@media screen and (device-aspect-ratio: 1280/720) { … }
@media screen and (device-aspect-ratio: 2560/1440) { … }

4.8. color

Value:
<integer>
Applies to: visual media types
Accept min/max prefixes: yes

The ‘color’ media feature describes
the number of bits per color component of the output device. If the device
is not a color device, the value is zero.

A specified <integer> cannot be negative.

@media all and (color) { … }
@media all and (min-color: 1) { … }

@media all and (min-color: 2) { … }

If different color components are represented by different number of
bits, the smallest number is used.

For instance, if an 8-bit color system represents the red component
with 3 bits, the green component with 3 bits and the blue component with
2 bits, the ‘color’ media feature will
have a value of 2.

In a device with indexed colors, the minimum number of bits per color
component in the lookup table is used.

The described functionality is only able to describe color
capabilities at a superficial level. If further functionality is required,
RFC2531 [RFC2531]
provides more specific media features which may be supported at a later
stage.

4.9. color-index

Value:
<integer>
Applies to: visual media types
Accepts min/max prefixes: yes

The ‘color-index’ media feature
describes the number of entries in the color lookup table of the output
device. If the device does not use a color lookup table, the value is
zero.

A specified <integer> cannot be negative.

@media all and (color-index) { … }
@media all and (min-color-index: 1) { … }

<?xml-stylesheet media="all and (min-color-index: 256)"
  href="http://www.example.com/…" ?>

4.10. monochrome

Value:
<integer>
Applies to: visual media types
Accepts min/max prefixes: yes

The ‘monochrome’ media feature
describes the number of bits per pixel in a monochrome frame buffer. If
the device is not a monochrome device, the output device value will be 0.

A specified <integer> cannot be negative.

@media all and (monochrome) { … }
@media all and (min-monochrome: 1) { … }

@media all and (min-monochrome: 2) { … }

<link rel="stylesheet" media="print and (color)" href="http://…" />
<link rel="stylesheet" media="print and (monochrome)" href="http://…" />

4.11. resolution

Value:
<resolution>
Applies to: bitmap media types
Accepts min/max prefixes: yes

The ‘resolution’ media feature
describes the resolution of the output device, i.e. the density of the
pixels. When querying devices with non-square pixels, in ‘min-resolution’ queries the least-dense dimension
must be compared to the specified value and in ‘max-resolution’ queries the most-dense dimensions
must be compared instead. A ‘resolution’ (without a «min-» or «max-» prefix)
query never matches a device with non-square pixels.

For printers, this corresponds to the screening resolution (the
resolution for printing dots of arbitrary color).

@media print and (min-resolution: 300dpi) { … }

@media print and (min-resolution: 118dpcm) { … }

4.12. scan

Value: progressive |
interlace
Applies to: «tv» media types
Accepts min/max prefixes: no

The ‘scan’ media feature describes
the scanning process of «tv» output devices.

@media tv and (scan: progressive) { … }

4.13. grid

Value:
<integer>
Applies to: visual and tactile media types
Accepts min/max prefixes: no

The ‘grid’ media feature is used to
query whether the output device is grid or bitmap. If the output device is
grid-based (e.g., a «tty» terminal, or a phone display with only one fixed
font), the value will be 1. Otherwise, the value will be 0.

Only 0 and 1 are valid values. (This includes -0.) Thus everything else
creates a malformed media query.

@media handheld and (grid) and (max-width: 15em) { … }
@media handheld and (grid) and (max-device-height: 7em) { … }

5. Values

This specification also introduces two new values.

The <ratio> value is a positive (not zero or negative) <integer>
followed by optional whitespace, followed by a solidus (‘/’), followed by optional whitespace, followed by a
positive <integer>.

The <resolution> value is a positive <number> immediately followed
by a unit identifier (‘dpi’ or
‘dpcm’).

Whitespace, <integer>, <number> and other values used by this
specification are the same as in other parts of CSS, normatively defined
by CSS 2.1. [CSS21]

6. Units

The units used in media queries are the same as in other parts of CSS.
For example, the pixel unit represents CSS pixels and not physical pixels.

Relative units in media queries are based on the initial value, which
means that units are never based on results of declarations. For example,
in HTML, the ‘em’ unit is relative to
the initial value of ‘font-size’.

6.1. Resolution

The ‘dpi’ and ‘dpcm’ units describe the resolution of an output
device, i.e., the density of device pixels. Resolution unit identifiers
are:

dpi

dots per CSS ‘inch’

dpcm

dots per CSS ‘centimeter’

In this specification, these units are only used in the ‘resolution’ media feature.

7. Changes

7.1. Changes Since the 19 June 2012
Recommendation

Proposed Corrections were introduced:

• Proposed Correction 1 in Section 3.1:
  Clarify that the keywords ‘not’, ‘and’, ‘only’, and ‘or’ should not be treated as unknown media types,
  but as syntax errors when used in place of media types.

A handful of editorial and markup corrections were also made:

• Section 2: Dropped a redundant attribute in an example.
  

  <link rel="stylesheet" media="screen and (color), projection and (color)" rel="stylesheet" href="example.css">

  <link rel="stylesheet" media="screen and (color), projection and (color)" rel="stylesheet" href="example.css" />

• Section 2: Adjusted a sentence to make it easier for other specifications to extend this one.
  

  To avoid circular dependencies, it is neverunless another feature explicitly specifies that it affects the resolution of Media Queries, it is not necessary to apply the style sheet in order to evaluate expressions.

• Section 3: Used a more precise term to characterize the syntax of css,
  in a descriptive (rather than prescriptive) sentence.

  CSS style sheets are generally case-insensitive
  ASCII case-insensitive,
  and this is also the case for media queries.

  The veracity of this claim is validated by a test.

• Section 4.13: Corrected a syntax error in an example.
  

  @media handheld and (grid) and (device-max-heightmax-device-height: 7em) { … }

• Bibliographical references have been updated to point to the latest versions.
• Various links throughout the specification were updated from http to https.

7.2. Changes Since the 27 July
2010 Candidate Recommendation

The following changes were made to this specification since the 27 July
2010 Candidate Recommendation:

• Section 4.11: Clarified the meaning of
  resolution in the case of printers, for which the meaning of dots was
  ambiguous.

  For printers, this corresponds to the screening resolution (the
  resolution for printing dots of arbitrary color).

• Section 6.1: Made it explicit that the
  ‘inch’ and ‘cm’ mentioned are the CSS units, not the physical
  ones.

  dpi

  dots per CSS ‘inch’inch

  dpcm

  dots per CSS ‘centimeter’cm

• Section 4.1: Adjust mistaken non normative
  wording to match correct normative wording from Section
  6.

  The ‘em’ value is relative to the
  font size of the root elementinitial value of
  ‘font-size’..

• Section 6: Clarify that units are never based on
  the results of declarations.

  Relative units in media queries are based on the initial value,
  which means that units are never based on results of
  declarations. For example, in HTML, the ‘em’ unit is relative to the initial value of
  ‘font-size’.

Acknowledgments

This specification is the product of the W3C Working Group on Cascading
Style Sheets.

Comments from Björn Höhrmann, Christoph Päper, Chris
Lilley, Simon Pieters, Rijk van Geijtenbeek, Sigurd Lerstad, Arve
Bersvendsen, Susan Lesch, Philipp Hoschka, Roger Gimson, Steven Pemberton,
Simon Kissane, Melinda Grant, and L. David Baron improved this
specification.

References

Normative references

[CSS21]

Bert Bos; et al. Cascading Style
Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June
2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-CSS2-20110607

Other references

[HTML401]

Dave Raggett; Arnaud Le Hors; Ian Jacobs. HTML 4.01
Specification. 24 December 1999, superseded 27 March 2018. W3C Recommendation. URL: https://www.w3.org/TR/2018/SPSD-html401-20180327/

[HTML]

Anne van Kesteren; et al. HTML
Standard. Living Standard. URL: https://html.spec.whatwg.org/multipage/

[RFC2531]

G. Klyne; L. McIntyre. Content Feature Schema
for Internet Fax. March 1999. Internet RFC 2531. URL: http://www.ietf.org/rfc/rfc2531.txt

[XMLSTYLE]

James Clark; Simon Pieters; Henry S. Thompson Associating Style Sheets
with XML documents 1.0 (Second Edition) 28 October 2010. W3C
Recommendation. URL: http://www.w3.org/TR/2010/REC-xml-stylesheet-20101028/