csswg-drafts/css2/diffs-rec/media.html at 7c55056f3aadd7fe6111e59b0639f23f7fc1f1d3 · w3c/csswg-drafts · GitHub

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">

<HEAD>
<TITLE>Media types</TITLE>
<link rel="stylesheet" href="style/default.css" type="text/css">
<link rel="stylesheet" href="http://www.w3.org/StyleSheets/TR/W3C-CR.css" type="text/css">
<link rel="prev" href="cascade.html">
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<link rel="contents" href="cover.html#minitoc">
<link rel="CSS-properties" href="propidx.html" title="properties">
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</HEAD>
<BODY>
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<hr class="navbar">

<H1><a name="q0">7 Media types</a></H1>
<div class="subtoc">
<p><strong>Contents</strong>
  <ul class="toc">
    <li class="tocline2"><a href="media.html#media-intro" class="tocxref">7.1 Introduction to media types</a>
    <li class="tocline2"><a href="media.html#media-sheets" class="tocxref">7.2 Specifying media-dependent style sheets</a>
    <ul class="toc">
      <li class="tocline3"><a href="media.html#at-media-rule" class="tocxref">7.2.1 The @media rule</a>
    </ul>
    <li class="tocline2"><a href="media.html#media-types" class="tocxref">7.3 Recognized media types</a>
    <ul class="toc">
      <li class="tocline3"><a href="media.html#media-groups" class="tocxref">7.3.1 Media groups</a>
    </ul>
  </ul>
</div>

<H2>7.1 <a name="media-intro">Introduction to media types</a></H2>

<P>One of the most important features of style sheets is that they
specify how a document is to be presented on different media: on the
screen, on paper, with a speech synthesizer, with a braille device,
etc.

<P>Certain CSS properties are only designed for certain media (e.g.,
the <a href="page.html#propdef-page-break-before" class="noxref"
F440
><span
class="propinst-page-break-before"> <del>'cue-before'</del><ins>'page-break-before'</ins></span></a> property
 <del>for aural user agents).</del><ins>only applies to paged media).</ins> On occasion, however, style sheets for
different media types may share a property, but require different
values for that property. For example, the <a href="fonts.html#propdef-font-size" class="noxref"><span
class="propinst-font-size">'font-size'</span></a> property is useful both
for screen and print media.  <del>However,</del>The two media <ins>types</ins> are different enough
to require different values for the common property; a document will
typically need a larger font on a computer screen than on paper.
 <del>Experience also shows that sans-serif fonts are easier to read on screen, while fonts with serifs are easier to read on paper. For these reasons,</del><ins>Therefore,</ins> it is necessary to express that a style  <del>sheet --</del><ins>sheet,</ins> or a
section of a style  <del>sheet --</del><ins>sheet,</ins> applies to certain media types.

<H2>7.2 <a name="media-sheets">Specifying media-dependent style sheets</a></H2>
<P>There are currently two ways to specify media dependencies for
style sheets:</p>

<UL>

<LI>Specify the target medium from a style sheet with the <a name="x0"><span
	    class="index-inst" title="@media">@media</span></a> or <a name="x1"><span
	    class="index-inst" title="@import">@import</span></a> at-rules.

<div class="example"><P style="display:none">Example(s):</P>
<PRE>
@import  <del>url("loudvoice.css") aural;</del><ins>url("fancyfonts.css") screen;</ins>
@media print {
  /* style sheet for print goes here */
}
</PRE>
</div>

<LI>Specify the target medium within the document language. For
example, in HTML  <del>4.0</del><ins>4</ins> (<a href="refs.html#ref-HTML4" rel="biblioentry" class="noxref"><span class="informref"> <del>[HTML40]</del><ins>[HTML4]</ins></span></a>), the "media" attribute on the LINK
element specifies the target media of an external style sheet:

<div class="html-example">

<PRE>
&lt;!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML  <del>4.0//EN"&gt;</del><ins>4.01//EN"&gt;</ins>
&lt;HTML&gt;
   &lt;HEAD&gt;
      &lt;TITLE&gt;Link to a target medium&lt;/TITLE&gt;
      &lt;LINK REL="stylesheet" TYPE="text/css"
	 MEDIA="print, handheld" HREF="foo.css"&gt;
   &lt;/HEAD&gt;
   &lt;BODY&gt;
      &lt;P&gt;The body...
   &lt;/BODY&gt;
&lt;/HTML&gt;
</PRE>
</div>
</UL>

<p>The <a href="cascade.html#at-import">@import</a> rule is defined in
the <a href="cascade.html">chapter on the cascade</a>.


<H3>7.2.1 <a name="at-media-rule">The @media rule</a></H3>

<P>An <a name="x2"><span class="index-def" title="media">@media</span></a> rule
specifies the target <a href="#media-types">media types</a> (separated
by commas) of a set of <a
href="syndata.html#tokenization"> <del>rules</del><ins>statements</ins></a> (delimited by curly
braces). <ins>Invalid statements must be ignored per</ins> <a
href="syndata.html#rule-sets"><ins>4.1.7 "Rule sets, declaration blocks,
and selectors"</ins></a> <ins>and</ins> <a href="syndata.html#parsing-errors"><ins>4.2
"Rules for handling parsing errors."</ins></a> The <a name="x3"><span
class="index-inst" title="@media">@media</span></a> construct allows style
sheet rules for various media in the same style sheet:</P>

<pre class="example">
  @media print {
    body { font-size: 10pt }
  }
  @media screen {
    body { font-size:  <del>12pt</del><ins>13px</ins> }
  }
  @media screen, print {
    body { line-height: 1.2 }
  }
</pre>

<p> <del>7.3 Recognized media types A CSS media type names a set of CSS properties. A user agent that claims to support a media type by name must implement all</del><ins>Style rules outside</ins> of  <del>the properties that</del><ins>@media rules</ins> apply to <ins>all media types</ins>
that <ins>the style sheet applies to. At-rules inside @media are invalid in
CSS2.1.</ins>

<H2><ins>7.3</ins> <a name="media-types"><ins>Recognized</ins> media  <del>type.</del><ins>types</ins></a></H2>


<P>The names chosen for CSS media types reflect target devices for
which the relevant properties make sense. In the following list of CSS
media  <del>types,</del><ins>types the names of media types are normative, but</ins> the
 <del>parenthetical</del>descriptions are  <del>not normative. They only give a sense of what device</del><ins>informative. Likewise,</ins> the  <del>media type</del><ins>"Media" field in the
description of each property</ins> is  <del>meant to refer to.</del><ins>informative.</ins>

<dl>
<dt><strong>all</strong>
<dd>Suitable for all devices.


<dt><strong> <del>aural Intended for speech synthesizers. See the section on aural style sheets for details.</del>braille</strong>
<dd>Intended for braille tactile feedback devices.

<dt><strong>embossed</strong>
<dd>Intended for paged braille printers.

<dt><strong>handheld</strong>
<dd>Intended for handheld devices (typically small
screen,  <del>monochrome,</del>limited bandwidth).

<dt><strong>print</strong>
<dd>Intended for  <del>paged, opaque</del><ins>paged</ins> material and for documents viewed on
screen in print preview mode.  Please consult the section on <a
href="page.html">paged media</a> for information about formatting
issues that are specific to paged media.

<dt><strong>projection</strong>
<dd>Intended for projected presentations, for example  <del>projectors or print to transparencies.</del><ins>projectors.</ins>
Please consult the section on <a href="page.html">paged media</a> for
information about formatting issues that are specific to paged media.

<dt><strong>screen</strong>
<dd>Intended primarily for color computer screens.

<dt><strong><ins>speech</ins></strong>
<dd><ins>Intended for speech synthesizers. Note: CSS2 had a similar media type
called 'aural' for this purpose.  See the appendix on</ins>
<a href="./aural.html"><ins>aural style sheets</ins></a> <ins>for details.</ins>

<dt><strong>tty</strong>
<dd>Intended for media using a fixed-pitch character  <del>grid, such</del><ins>grid (such</ins> as
teletypes, terminals, or portable devices with limited display
 <del>capabilities.</del><ins>capabilities).</ins> Authors should not use <a
href="syndata.html#pixel-units">pixel units</a> with the "tty" media
type.

<dt><strong>tv</strong>
<dd>Intended for television-type devices (low
resolution, color, limited-scrollability screens, sound available).
</dl>

<P>Media type names are case-insensitive.

<P> <del>Due to rapidly changing technologies, CSS2 does not specify a definitive list of</del>Media types <ins>are mutually exclusive in the sense</ins> that <ins>a user agent can
only support one media type when rendering a document. However, user
agents may use different media types on different canvases. For
example, a document</ins> may <ins>(simultaneously)</ins> be  <del>values</del><ins>shown in 'screen' mode on
one canvas and 'print' mode on another canvas.</ins>

<p><ins>Note that a multimodal media type is still only one media
type. The 'tv' media type,</ins> for <ins>example, is a multimodal media
type that renders both visually and aurally to a single canvas.</ins>

<p>@media  <del>.</del><ins>and @import rules with unknown media types are treated as if
the unknown media types are not present.</ins>

<div class="example"><P style="display:none"><ins>Example(s):</ins></P>
<p><ins>For example, in the following snippet, the rule on the P element applies
in 'screen' mode (even though the '3D' media type is not known).</ins>

<pre>
<ins>@media screen, 3D {
  P { color: green; }
}</ins>
</pre>
</div>


<div class="note"><P>
<em><strong>Note.</strong>
Future  <del>versions</del><ins>updates</ins> of CSS may extend  <del>this list.</del><ins>the list of media types.</ins> Authors
should not rely on media type names that are not yet defined
by a CSS specification.
</em>
</div>

<H3>7.3.1 <a name="media-groups">Media groups</a></H3>

<P><em><ins>This section is informative, not normative.</ins></em></P>

<P>Each CSS property definition specifies  <del>the</del><ins>which</ins> media types  <del>for which</del>the
property  <del>must be implemented by a conforming user agent .</del><ins>applies to.</ins> Since properties generally apply to several  <del>media,</del><ins>media
types,</ins> the "Applies to media" section of each property definition
lists <a name="x4"><span class="index-def" title="media group">media groups</span></a>
rather than individual media types. Each property applies to all media
types in the media groups listed in its definition.

<P> <del>CSS2</del><ins>CSS&nbsp;2.1</ins> defines the following media groups: </P>
<ul>
<li>
<span class="index-def" title="'continuous' media group"><a
name="continuous-media-group"><strong>continuous</strong></a></span>
or <span class="index-def" title="'paged' media group"><a
name="paged-media-group"><strong>paged</strong></a></span>.

<li><span
class="index-def" title="'visual' media group"><a
name="visual-media-group"> <strong> <del>"Both" means that the property in question applies to both media groups.</del>visual</strong></a>,</span>
<span class="index-def" title="'audio' media group"><a
name="audio-media-group"><strong> <del>aural</del><ins>audio</ins></strong></a><ins>,</ins></span>
<span class="index-def" title="'speech' media group"><a
name="speech-media-group"><strong><ins>speech</ins></strong></a>,</span>
or <span
class="index-def" title="'tactile' media group"><a
name="tactile-media-group"><strong>tactile</strong></a></span>.
<li><span
class="index-def" title="'grid' media group"><a
name="grid-media-group"><strong>grid</strong></a></span> (for
character grid devices), or
<span
class="index-def" title="'bitmap' media group"><a
name="bitmap-media-group"><strong>bitmap</strong></a></span>.

<li><span
class="index-def" title="'interactive media group"><a
name="interactive-media-group"><strong> <del>"Both" means that the property in question applies to both media groups.</del>interactive</strong></a></span> (for
devices that allow user interaction), or
<span
name="static-media-group"><strong>static</strong></a></span> (for
those that  <del>don't). "Both" means that the property in question applies to both media groups.</del><ins>do not).</ins>

<li><span class="index-def" title="'all'
media group"> <a name="all-media-group"><strong>all</strong></a></span>
(includes all media types)
</ul>

<P>The following table shows the relationships
between media groups and media types:</P>

<TABLE border=1
       summary="Relationship between media groups and media types">
<CAPTION>Relationship between media groups and media types</CAPTION>
<TR><TH>Media Types <TH colspan="4">Media Groups
<TR><TH>&nbsp;
    <TH>continuous/paged
    <TH> <del>visual/aural/tactile</del><ins>visual/audio/speech/tactile</ins>
    <TH>grid/bitmap
    <TH>interactive/static

<TR><TH> <del>aural continuous aural N/A both</del>braille<TD align="center">continuous<TD align="center">tactile<TD align="center">grid<TD align="center">both</TR>
<TR><TH> <del>emboss</del><ins>embossed</ins><TD align="center">paged<TD align="center">tactile<TD align="center">grid<TD align="center"> <del>both</del><ins>static</ins></TR>
<TR><TH>handheld<TD align="center">both<TD align="center"> <del>visual</del><ins>visual, audio, speech</ins><TD
align="center">both<TD align="center">both</TR>
<TR><TH>print<TD align="center">paged<TD align="center">visual<TD
align="center">bitmap<TD align="center">static</TR>
<TR><TH>projection<TD align="center">paged<TD align="center">visual<TD align="center">bitmap<TD align="center"> <del>static</del><ins>interactive</ins></TR>
<TR><TH>screen<TD align="center">continuous<TD align="center"> <del>visual</del><ins>visual, audio</ins><TD align="center">bitmap<TD align="center">both</TR>
<TR><TH><ins>speech</ins><TD align="center"><ins>continuous</ins><TD align="center"><ins>speech</ins><TD align="center"><ins>N/A</ins><TD align="center"><ins>both</ins></TR>
<TR><TH>tty<TD align="center">continuous<TD align="center">visual<TD align="center">grid<TD align="center">both</TR>
<TR><TH>tv<TD align="center">both<TD align="center">visual,  <del>aural</del><ins>audio</ins><TD align="center">bitmap<TD align="center">both</TR>
</TABLE>

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