csswg-drafts/css2/diffs-rec/media.html at 635649a32e6647a3079544114dc1273920d3e97d · w3c/csswg-drafts · GitHub

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

<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<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-WD.css" type="text/css">
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<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#q1" class="tocxref">7.1 Introduction to media types</a>
    <li class="tocline2"><a href="media.html#q2" 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><a name="q1">7.1 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"><span
class="propinst-page-break-before"> <del>'cue-before'</del><ins>'page-break-before'</ins></span></a> property
 <del>for</del> <del>aural</del> <del>user</del> <del>agents).</del><ins>only</ins> <ins>applies</ins> <ins>to</ins> <ins>paged</ins> <ins>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</del> <del>also</del> <del>shows</del> <del>that</del> <del>sans-serif</del> <del>fonts</del> <del>are</del> <del>easier</del> <del>to</del> <del>read</del> <del>on</del> <del>screen,</del> <del>while</del> <del>fonts</del> <del>with</del> <del>serifs</del> <del>are</del> <del>easier</del> <del>to</del> <del>read</del> <del>on</del> <del>paper.</del> <del>For</del> <del>these</del> <del>reasons,</del><ins>Therefore,</ins> it is necessary to express that a style  <del>sheet</del> <del>--</del><ins>sheet,</ins> or a
section of a style  <del>sheet</del> <del>--</del><ins>sheet,</ins> applies to certain media types.

<H2><a name="q2">7.2 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")</del> <del>aural;</del><ins>url("fancyfonts.css")</ins> <ins>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 rules (delimited by curly braces).  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>


<H2>7.3 <a name="media-types">Recognized media types</a></H2>


<P> <del>A</del> <del>CSS</del> <del>media</del> <del>type</del> <del>names</del> <del>a</del> <del>set</del> <del>of</del> <del>CSS</del> <del>properties.</del> <del>A</del> <del>user</del> <del>agent</del> <del>that</del> <del>claims</del> <del>to</del> <del>support</del> <del>a</del> <del>media</del> <del>type</del> <del>by</del> <del>name</del> <del>must</del> <del>implement</del> <del>all</del> <del>of</del> <del>the</del> <del>properties</del> <del>that</del> <del>apply</del> <del>to</del> <del>that</del> <del>media</del> <del>type.</del>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</ins> <ins>the</ins> <ins>names</ins> <ins>of</ins> <ins>media</ins> <ins>types</ins> <ins>are</ins> <ins>normative,</ins> <ins>but</ins> the
 <del>parenthetical</del>descriptions are  <del>not</del> <del>normative.</del> <del>They</del> <del>only</del> <del>give</del> <del>a</del> <del>sense</del> <del>of</del> <del>what</del> <del>device</del><ins>informative.</ins> <ins>Likewise,</ins> the  <del>media</del> <del>type</del><ins>"Media"</ins> <ins>field</ins> <ins>in</ins> <ins>the</ins>
<ins>description</ins> <ins>of</ins> <ins>each</ins> <ins>property</ins> is  <del>meant</del> <del>to</del> <del>refer</del> <del>to.</del><ins>informative.</ins>

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


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

<dt><strong>embossed</strong>

<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,</del> <del>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</del> <del>or</del> <del>print</del> <del>to</del> <del>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</ins> <ins>for</ins> <ins>speech</ins> <ins>synthesizers.</ins> <ins>Note:</ins> <ins>CSS2</ins> <ins>had</ins> <ins>a</ins> <ins>similar</ins> <ins>media</ins> <ins>type</ins>
<ins>called</ins> <ins>'aural'</ins> <ins>for</ins> <ins>this</ins> <ins>purpose.</ins>  <ins>See</ins> <ins>the</ins> <ins>appendix</ins> <ins>on</ins>
<a href="./aural.html"><ins>aural</ins> <ins>style</ins> <ins>sheets</ins></a> <ins>for</ins> <ins>details.</ins>

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

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


<P><ins>Unknown</ins> <ins>media</ins> <ins>type</ins> <ins>names</ins> <ins>must</ins> <ins>not</ins> <ins>result</ins> <ins>in</ins> <ins>the</ins> @media  <del>.</del><ins>rule</ins> <ins>being</ins> <ins>ignored.</ins>


<div class="note"><P>
<em><strong>Note.</strong>
Future  <del>versions</del><ins>updates</ins> of CSS may extend  <del>this</del> <del>list.</del><ins>the</ins> <ins>list</ins> <ins>of</ins> <ins>media</ins> <ins>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</ins> <ins>section</ins> <ins>is</ins> <ins>informative,</ins> <ins>not</ins> <ins>normative.</ins></em></P>

<P>Each CSS property definition specifies  <del>the</del><ins>which</ins> media types  <del>for</del> <del>which</del>the
property  <del>must</del> <del>be</del> <del>implemented</del> <del>by</del> <del>a</del> <del>conforming</del> <del>user</del> <del>agent</del> <del>.</del><ins>applies</ins> <ins>to.</ins> Since properties generally apply to several  <del>media,</del><ins>media</ins>
<ins>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"</del> <del>means</del> <del>that</del> <del>the</del> <del>property</del> <del>in</del> <del>question</del> <del>applies</del> <del>to</del> <del>both</del> <del>media</del> <del>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"</del> <del>means</del> <del>that</del> <del>the</del> <del>property</del> <del>in</del> <del>question</del> <del>applies</del> <del>to</del> <del>both</del> <del>media</del> <del>groups.</del>interactive</strong></a></span> (for
devices that allow user interaction), or
<span
class="index-def" title="'static' media group"><a
name="static-media-group"><strong>static</strong></a></span> (for
those that don't).

<li><span class="index-def" title="'all'
media group"> <a name="all-media-group"><strong> <del>"Both"</del> <del>means</del> <del>that</del> <del>the</del> <del>property</del> <del>in</del> <del>question</del> <del>applies</del> <del>to</del> <del>both</del> <del>media</del> <del>groups.</del>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</del> <del>continuous</del> <del>aural</del> <del>N/A</del> <del>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,</ins> <ins>audio,</ins> <ins>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,</ins> <ins>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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