discontinued / server · Files

WD-css3-speech-20110818 141 KB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">

<html lang=en>
 <head>
  <title>CSS Speech Module</title>
  <meta content="text/html; charset=utf-8" http-equiv=Content-Type>
  <link href=default.css rel=stylesheet type="text/css">

  <style type="text/css">
      p
      {
          padding-bottom : 1em;
      }
      
      p + p
      {
          text-indent : 0;
      }
      
      *:target
      {
          border : 1px dashed #66CC66;
      }</style>
  <!--
      .prod
      {
      font-family : inherit;
      font-size : inherit
      }
      
      pre.prod
      {
      white-space : pre-wrap;
      margin : 1em 0 1em 2em
      }
      
      code
      {
      font-size : inherit;
      }
      
      #box-shadow-samples td
      {
      background : white;
      color : black;
      }
      
      caption
      {
      text-align : left;
      font-weight : bold
      }
      
      .note
      {
      font-style : italic
      }
      
      .issue
      {
      color : maroon;
      font-style : italic
      }
      
      div.example pre
      {
      color : green;
      margin-left : 2em
      }
      
      dl
      {
      margin-left : 2em
      }
      
      caption dfn
      {
      font-size : 120%
      }
    -->
  <link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel=stylesheet
  type="text/css">

 <body>
  <div class=head> <!--begin-logo-->
   <p><a href="http://www.w3.org/"><img alt=W3C height=48
    src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->

   <h1 id=top>CSS Speech Module</h1>

   <h2 class="no-num no-toc" id=longstatus-date>W3C Working Draft 18 August
    2011</h2>

   <dl>
    <dt>This version:

    <dd> <a
     href="http://www.w3.org/TR/2011/WD-css3-speech-20110818">http://www.w3.org/TR/2011/WD-css3-speech-20110818</a>
     

    <dt>Latest version:

    <dd> <a
     href="http://www.w3.org/TR/css3-speech">http://www.w3.org/TR/css3-speech</a>
     

    <dt>Previous versions:

    <dd> <a
     href="http://www.w3.org/TR/2011/WD-css3-speech-20110419">http://www.w3.org/TR/2011/WD-css3-speech-20110419</a>
     

    <dt id=editors-list>Editor:

    <dd><a href="mailto:dweck@daisy.org">Daniel Weck</a> (<a
     href="http://www.daisy.org">DAISY Consortium</a>)

    <dt>Former editors:

    <dd><a href="mailto:dsr@w3.org">Dave Raggett</a> (<a
     href="http://www.w3.org/">W3C</a>/<a
     href="http://www.canon.com/">Canon</a>)

    <dd><a href="mailto:daniel@glazman.org">Daniel Glazman</a> (<a
     href="http://www.disruptive-innovations.com/">Disruptive
     Innovations</a>)

    <dd><a href="mailto:csant@opera.com">Claudio Santambrogio</a> (<a
     href="http://www.opera.com/">Opera Software</a>)
   </dl>
   <!--begin-copyright-->
   <p class=copyright><a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
    rel=license>Copyright</a> &copy; 2011 <a
    href="http://www.w3.org/"><acronym title="World Wide Web
    Consortium">W3C</acronym></a><sup>&reg;</sup> (<a
    href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
    of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym
    title="European Research Consortium for Informatics and
    Mathematics">ERCIM</acronym></a>, <a
    href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
    <a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
    and <a
    href="http://www.w3.org/Consortium/Legal/copyright-documents">document
    use</a> rules apply.</p>
   <!--end-copyright-->
   <hr title="Separator for header">
  </div>

  <h2 class="no-num no-toc" id=abstract>Abstract</h2>

  <p>CSS (Cascading Style Sheets) is a language that describes the rendering
   of markup documents (e.g. HTML, XML) on various supports, such as screen,
   paper, speech, etc. The Speech module defines aural CSS properties that
   enable authors to declaratively control the rendering of documents via
   speech synthesis, and using optional audio cues. The feature set exposed
   by this specification is designed to match the model described by the
   Speech Synthesis Markup Language (SSML) Version 1.1 <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>. Note that this standard was
   developed in cooperation with the <a href="http://www.w3.org/Voice/">Voice
   Browser Activity</a>.

  <h2 class="no-num no-toc" id=status>Status of this document</h2>
  <!--begin-status-->

  <p><em>This section describes the status of this document at the time of
   its publication. Other documents may supersede this document. A list of
   current W3C publications and the latest revision of this technical report
   can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
   index at http://www.w3.org/TR/.</a></em>

  <p>Publication as a Working Draft does not imply endorsement by the W3C
   Membership. This is a draft document and may be updated, replaced or
   obsoleted by other documents at any time. It is inappropriate to cite this
   document as other than work in progress.

  <p>The (<a
   href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
   mailing list <a href="mailto:www-style@w3.org">www-style@w3.org</a> (see
   <a href="http://www.w3.org/Mail/Request">instructions</a>) is preferred
   for discussion of this specification. When sending e-mail, please put the
   text &#8220;css3-speech&#8221; in the subject, preferably like this:
   &#8220;[<!---->css3-speech<!---->] <em>&hellip;summary of
   comment&hellip;</em>&#8221;

  <p>This document was produced by the <a
   href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of
   the <a href="http://www.w3.org/Style/">Style Activity</a>).

  <p>This document was produced by a group operating under the <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
   2004 W3C Patent Policy</a>. W3C maintains a <a
   href="http://www.w3.org/2004/01/pp-impl/32061/status"
   rel=disclosure>public list of any patent disclosures</a> 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 <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
   Claim(s)</a> must disclose the information in accordance with <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
   6 of the W3C Patent Policy</a>.</p>
  <!--end-status-->

  <p>This is a “last call” working draft, i.e., the working group expects
   this to be the last call for comments before the document becomes a W3C
   Candidate Recommendation. The <strong>deadline for comments</strong> is
   <strong>30 September 2011</strong>.</p>
  <!-- div class="issue">
      <p>The following issues need to be discussed and require working group resolutions:</p>
      <ul>
        <li>
          <a href="#issue-xxx">xxx</a>
        </li>
      </ul>
      <p>The CSS WG maintains a separate <a href="http://www.w3.org/Style/CSS/Tracker/products/29"
          >list of issues</a> for this module.</p>
          </div -->

  <p>The following features are at-risk and may be dropped at the end of the
   CR period if there has not been enough interest from implementers:
   &lsquo;<a href="#voice-balance"><code
   class=property>voice-balance</code></a>&rsquo;, &lsquo;<a
   href="#voice-duration"><code
   class=property>voice-duration</code></a>&rsquo;, &lsquo;<a
   href="#voice-pitch"><code class=property>voice-pitch</code></a>&rsquo;,
   &lsquo;<a href="#voice-range"><code
   class=property>voice-range</code></a>&rsquo;, and &lsquo;<a
   href="#voice-stress"><code class=property>voice-stress</code></a>&rsquo;.

  <p>The CSS Speech module is a community effort and if you would like to
   help with implementation and driving the specification forward along the
   W3C Recommendation track, please contact the editors.

  <h2 class="no-num no-toc" id=contents>Table of contents</h2>
  <!--begin-toc-->

  <ul class=toc>
   <li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
    <ul class=toc>
     <li><a href="#design-goals"><span class=secno>1.1. </span>Design goals,
      motivations</a>

     <li><a href="#css21-rel"><span class=secno>1.2. </span>Relationship with
      CSS2.1</a>
    </ul>

   <li><a href="#values"><span class=secno>2. </span>CSS values</a>

   <li><a href="#example"><span class=secno>3. </span>Example</a>

   <li><a href="#aural-model"><span class=secno>4. </span>The aural
    formatting model</a>

   <li><a href="#mixing-props"><span class=secno>5. </span>Mixing
    properties</a>
    <ul class=toc>
     <li><a href="#mixing-props-voice-volume"><span class=secno>5.1.
      </span>The &lsquo;<code class=property>voice-volume</code>&rsquo;
      property</a>

     <li><a href="#mixing-props-voice-balance"><span class=secno>5.2.
      </span>The &lsquo;<code class=property>voice-balance</code>&rsquo;
      property</a>
    </ul>

   <li><a href="#speaking-props"><span class=secno>6. </span>Speaking
    properties</a>
    <ul class=toc>
     <li><a href="#speaking-props-speak"><span class=secno>6.1. </span>The
      &lsquo;<code class=property>speak</code>&rsquo; property</a>

     <li><a href="#speaking-props-speak-as"><span class=secno>6.2. </span>The
      &lsquo;<code class=property>speak-as</code>&rsquo; property</a>
    </ul>

   <li><a href="#pause-props"><span class=secno>7. </span>Pause properties
    </a>
    <ul class=toc>
     <li><a href="#pause-props-pause-before-after"><span class=secno>7.1.
      </span>The &lsquo;<code class=property>pause-before</code>&rsquo; and
      &lsquo;<code class=property>pause-after</code>&rsquo; properties</a>

     <li><a href="#pause-props-pause"><span class=secno>7.2. </span>The
      &lsquo;<code class=property>pause</code>&rsquo; shorthand property</a>

     <li><a href="#collapsing"><span class=secno>7.3. </span>Collapsing
      pauses</a>
    </ul>

   <li><a href="#rest-props"><span class=secno>8. </span>Rest properties</a>
    <ul class=toc>
     <li><a href="#rest-props-rest-before-after"><span class=secno>8.1.
      </span>The &lsquo;<code class=property>rest-before</code>&rsquo; and
      &lsquo;<code class=property>rest-after</code>&rsquo; properties</a>

     <li><a href="#rest-props-rest"><span class=secno>8.2. </span>The
      &lsquo;<code class=property>rest</code>&rsquo; shorthand property</a>
    </ul>

   <li><a href="#cue-props"><span class=secno>9. </span>Cue properties</a>
    <ul class=toc>
     <li><a href="#cue-props-cue-before-after"><span class=secno>9.1.
      </span>The &lsquo;<code class=property>cue-before</code>&rsquo; and
      &lsquo;<code class=property>cue-after</code>&rsquo; properties</a>

     <li><a href="#cue-props-cue"><span class=secno>9.2. </span>The
      &lsquo;<code class=property>cue</code>&rsquo; shorthand property</a>
    </ul>

   <li><a href="#voice-char-props"><span class=secno>10. </span>Voice
    characteristic properties</a>
    <ul class=toc>
     <li><a href="#voice-props-voice-family"><span class=secno>10.1.
      </span>The &lsquo;<code class=property>voice-family</code>&rsquo;
      property</a>

     <li><a href="#voice-props-voice-rate"><span class=secno>10.2. </span>The
      &lsquo;<code class=property>voice-rate</code>&rsquo; property</a>

     <li><a href="#voice-props-voice-pitch"><span class=secno>10.3.
      </span>The &lsquo;<code class=property>voice-pitch</code>&rsquo;
      property</a>

     <li><a href="#voice-props-voice-range"><span class=secno>10.4.
      </span>The &lsquo;<code class=property>voice-range</code>&rsquo;
      property</a>

     <li><a href="#voice-props-voice-stress"><span class=secno>10.5.
      </span>The &lsquo;<code class=property>voice-stress</code>&rsquo;
      property</a>
    </ul>

   <li><a href="#duration-props"><span class=secno>11. </span>Voice duration
    property</a>
    <ul class=toc>
     <li><a href="#mixing-props-voice-duration"><span class=secno>11.1.
      </span>The &lsquo;<code class=property>voice-duration</code>&rsquo;
      property</a>
    </ul>

   <li><a href="#lists"><span class=secno>12. </span>List items and counters
    styles</a>

   <li><a href="#content"><span class=secno>13. </span>Inserted and replaced
    content</a>

   <li><a href="#pronunciation"><span class=secno>14. </span> Pronunciation,
    phonemes </a>

   <li class=no-num><a href="#property-index">Appendix A &mdash; Property
    index</a>

   <li class=no-num><a href="#index">Appendix B &mdash; Index</a>

   <li class=no-num><a href="#definitions">Appendix C &mdash; Definitions</a>
    
    <ul class=toc>
     <li class=no-num><a href="#glossary">Glossary</a>

     <li class=no-num><a href="#conformance">Conformance</a>

     <li class=no-num><a href="#exit">CR exit criteria</a>
    </ul>

   <li class=no-num><a href="#ack">Appendix D &mdash; Acknowledgements</a>

   <li class=no-num><a href="#changes">Appendix E &mdash; Changes from
    previous draft</a>

   <li class=no-num><a href="#references">Appendix F &mdash; References</a>
    <ul class=toc>
     <li class=no-num><a href="#normative-references">Normative
      references</a>

     <li class=no-num><a href="#other-references">Other references</a>
    </ul>
  </ul>
  <!--end-toc-->

  <h2 id=introduction><span class=secno>1. </span>Introduction</h2>

  <p class=note>Note that this entire section is non-normative.

  <h3 id=design-goals><span class=secno>1.1. </span>Design goals, motivations</h3>

  <p>The aural rendering of a document combines speech synthesis (also known
   as "TTS", the acronym for "Text to Speech") and auditory icons (which we
   refer to as "audio cues" in this specification). The aural presentation of
   information is common amongst communities of users who are blind or
   visually-impaired. For instance, "screen readers" enable control of visual
   user-interfaces that would otherwise be inaccessible. There are other
   cases whereby listening to textual information (as opposed to reading it)
   is a necessity. Typical examples include in-car use of an e-book reader,
   industrial and medical documentation systems, home entertainment, helping
   users to learn reading, or supporting users who have reading difficulties
   (print disabilities).

  <p> When it comes to documents, the quality of the speech rendition depends
   on the structure and semantics authored within the content itself. The CSS
   Speech module provides properties that enable authors to declaratively
   control presentational aspects of the aural dimension (e.g. TTS voice,
   pitch, rate, and volume levels). These style sheet properties can be used
   together with visual properties (mixed media), or as a complete aural
   alternative to a visual presentation.

  <p> Content creators can conditionally include CSS properties dedicated to
   user-agents with text to speech synthesis capabilities, by specifying the
   "speech" media type via the <code>media</code> attribute of the
   <code>link</code> element, or with the <code>@media</code> at-rule, or
   within an <code>@import</code> statement. When doing so, the styles
   authored within the scope of such conditional statements are ignored by
   user-agents that do not support this module.

  <h3 id=css21-rel><span class=secno>1.2. </span>Relationship with CSS2.1</h3>

  <p> The CSS Speech module is a re-work of the informative CSS2.1 Aural
   appendix, within which the "aural" media type was described, but also
   deprecated (in favor of the "speech" media type). Although the <a
   href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> specification
   reserves the "speech" media type, it doesn't actually define the
   corresponding properties. This module describes the CSS properties that
   apply to the "speech" media type, and defines a new "box" model
   specifically for the aural dimension.

  <h2 id=values><span class=secno>2. </span>CSS values</h2>

  <p>This specification follows the <a
   href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
   definition conventions</a> from <a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>. Value types not defined in
   this specification are defined in CSS Value and Units Level 3 <a
   href="#CSS3VAL" rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>.

  <p>In addition to the property-specific values listed in their definitions,
   all properties defined in this specification also accept the <a
   href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
   keyword as their property value. For readability it has not been repeated
   explicitly.

  <h2 id=example><span class=secno>3. </span>Example</h2>

  <div class=example>
   <p>This example shows how authors can tell the speech synthesizer to speak
    HTML headings with a voice called "paul", using "moderate" emphasis
    (which is more than normal) and how to insert an audio cue (pre-recorded
    audio clip located at the given URL) before the start of TTS rendering
    for each heading. In a stereo-capable sound system, paragraphs marked
    with the CSS class "heidi" are rendered on the left audio channel (and
    with a female voice, etc.), whilst the class "peter" corresponds to the
    right channel (and to a male voice, etc.). The volume level of text spans
    marked with the class "special" is lower than normal, and a prosodic
    boundary is created by introducing a strong pause after it is spoken
    (note how the <code>span</code> inherits the voice-family from its parent
    paragraph).</p>

   <pre>
h1, h2, h3, h4, h5, h6
{
  voice-family: paul;
  voice-stress: moderate;
  cue-before: url(../audio/ping.wav);
  voice-volume: medium 6dB;
}
p.heidi
{
  voice-family: female;
  voice-balance: left;
  voice-pitch: high;
  voice-volume: -6dB;
}
p.peter
{
  voice-family: male;
  voice-balance: right;
  voice-rate: fast;
}
span.special
{
  voice-volume: soft;
  pause-after: strong;
}

...

&lt;h1&gt;I am Paul, and I speak headings.&lt;/h1&gt;
&lt;p class="heidi"&gt;Hello, I am Heidi.&lt;/p&gt;
&lt;p class="peter"&gt;
  &lt;span class="special"&gt;Can you hear me ?&lt;/span&gt;
  I am Peter.
&lt;/p&gt;</pre>
  </div>

  <h2 id=aural-model><span class=secno>4. </span>The aural formatting model</h2>

  <p>The CSS formatting model for aural media is based on a sequence of
   sounds and silences that occur within a nested context similar to the <a
   href="#box-model-def">visual box model</a>, which we name the <dfn
   id=aural-box-model>aural "box" model</dfn>. The aural "canvas" consists of
   a two-channel (stereo) space and of a temporal dimension, within which
   synthetic speech and audio cues coexist. The selected element is
   surrounded by &lsquo;<a href="#rest"><code
   class=property>rest</code></a>&rsquo;, &lsquo;<a href="#cue"><code
   class=property>cue</code></a>&rsquo; and &lsquo;<a href="#pause"><code
   class=property>pause</code></a>&rsquo; properties (from the innermost to
   the outermost position). These can be seen as aural equivalents to
   &lsquo;<code class=property>padding</code>&rsquo;, &lsquo;<code
   class=property>border</code>&rsquo; and &lsquo;<code
   class=property>margin</code>&rsquo;, respectively. When used, the
   &lsquo;<code class=css>:before</code>&rsquo; and &lsquo;<code
   class=css>:after</code>&rsquo; pseudo-elements <a href="#CSS21"
   rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> get inserted between the
   element's contents and the &lsquo;<a href="#rest"><code
   class=property>rest</code></a>&rsquo;.

  <p> The following diagram illustrates the equivalence between properties of
   the visual and aural box models, applied to the selected &lt;element&gt;:

  <p> <img alt="A graph depicting the aural 'box' model." id=aural-box
   src=aural-box.png>

  <h2 id=mixing-props><span class=secno>5. </span>Mixing properties</h2>

  <h3 id=mixing-props-voice-volume><span class=secno>5.1. </span>The
   &lsquo;<a href="#voice-volume"><code
   class=property>voice-volume</code></a>&rsquo; property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=voice-volume>voice-volume</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>silent | [[x-soft | soft | medium | loud | x-loud] ||
      &lt;decibel&gt;]

    <tr>
     <td> <em>Initial:</em>

     <td>medium

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>a keyword value, and optionally also a decibel offset (if not zero)
  </table>

  <p>The &lsquo;<a href="#voice-volume"><code
   class=property>voice-volume</code></a>&rsquo; property allows authors to
   control the amplitude of the audio waveform generated by the speech
   synthesiser, and is also used to adjust the relative volume level of <a
   href="#cue-props">audio cues</a> within the <a href="#aural-model">audio
   "box" model</a>.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_prosody"><code>volume</code>
   attribute of the <code>prosody</code> element</a> from the SSML markup
   language <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl><!-- dt>
        <strong>normal</strong>
      </dt>
      <dd>
        <p> Corresponds to +0.0dB, which means that there is no modification of volume level. This
          value overrides the inherited value.</p>
      </dd -->

   <dt> <strong>silent</strong>

   <dd>
    <p> Specifies that no sound is generated (the text is read "silently").
     Corresponds to negative infinity in dB units.</p>

    <p class=note> Note that there is a difference between an element whose
     &lsquo;<a href="#voice-volume"><code
     class=property>voice-volume</code></a>&rsquo; property has a value of
     &lsquo;<code class=property>silent</code>&rsquo;, and an element whose
     &lsquo;<a href="#speak"><code class=property>speak</code></a>&rsquo;
     property has the value &lsquo;<code class=property>none</code>&rsquo;.
     With the former, the selected element takes up the same time as if it
     was spoken, including any pause before and after the element, but no
     sound is generated (descendants can override the &lsquo;<a
     href="#voice-volume"><code class=property>voice-volume</code></a>&rsquo;
     value and may therefore generate audio output). With the latter, the
     selected element is not rendered in the aural dimension and no time is
     allocated for playback (descendants can override the &lsquo;<a
     href="#speak"><code class=property>speak</code></a>&rsquo; value and may
     therefore generate audio output).</p>

   <dt><strong>x-soft</strong>, <strong>soft</strong>,
    <strong>medium</strong>, <strong>loud</strong>, <strong>x-loud</strong>

   <dd>
    <p> This sequence of keywords corresponds to monotonically non-decreasing
     volume levels, mapped to implementation-dependent values (i.e. inferred
     by the user-agent) that meet the user's requirements in terms of
     perceived sound loudness . The keyword &lsquo;<code
     class=property>x-soft</code>&rsquo; maps to the user's <em>minimum
     audible</em> volume level, &lsquo;<code
     class=property>x-loud</code>&rsquo; maps to the user's <em>maximum
     tolerable</em> volume level, &lsquo;<code
     class=property>medium</code>&rsquo; maps to the user's
     <em>preferred</em> volume level, &lsquo;<code
     class=property>soft</code>&rsquo; and &lsquo;<code
     class=property>loud</code>&rsquo; map to intermediary values.</p>

   <dt> <strong>&lt;decibel&gt;</strong>

   <dd>
    <p>A <a href="#number-def">number</a> immediately followed by "dB"
     (decibel unit). This represents a change (positive or negative) relative
     to the given keyword value (see enumeration above), or to the default
     value for the root element, or otherwise to the inherited volume level
     (which may itself be a combination of a keyword value and of a decibel
     offset, in which case the decibel values are combined additively). When
     the inherited volume level is &lsquo;<code
     class=property>silent</code>&rsquo;, this &lsquo;<a
     href="#voice-volume"><code class=property>voice-volume</code></a>&rsquo;
     resolves to &lsquo;<code class=property>silent</code>&rsquo; too,
     regardless of the specified &lt;decibel&gt; value. Decibels represent
     the ratio of the squares of the new signal amplitude (a1) and the
     current amplitude (a0), as per the following logarithmic equation:
     volume(dB) = 20 log10 (a1 / a0)</p>

    <p class=note> Note that -6.0dB is approximately half the amplitude of
     the audio signal, and +6.0dB is approximately twice the amplitude.</p>
  </dl>

  <p class=note>Note that the actual perceived volume levels depend on
   various factors, such as the listening environment and personal user
   preferences. The effective volume variation between &lsquo;<code
   class=property>x-soft</code>&rsquo; and &lsquo;<code
   class=property>x-loud</code>&rsquo; represents the dynamic range (in terms
   of loudness) of the speech output. Typically, this range would be
   compressed in a noisy context, i.e. the perceived loudness corresponding
   to &lsquo;<code class=property>x-soft</code>&rsquo; would effectively be
   closer to &lsquo;<code class=property>x-loud</code>&rsquo; than it would
   be in a quiet environment. There may also be situations where both
   &lsquo;<code class=property>x-soft</code>&rsquo; and &lsquo;<code
   class=property>x-loud</code>&rsquo; would map to low volume levels, such
   as in listening environments requiring discretion (e.g. library,
   night-reading).

  <h3 id=mixing-props-voice-balance><span class=secno>5.2. </span>The
   &lsquo;<a href="#voice-balance"><code
   class=property>voice-balance</code></a>&rsquo; property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=voice-balance>voice-balance</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;number&gt; | left | center | right | leftwards | rightwards

    <tr>
     <td> <em>Initial:</em>

     <td>center

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>the specified value resolved to a &lt;number&gt; between
      &lsquo;<code class=css>-100</code>&rsquo; and &lsquo;<code
      class=css>100</code>&rsquo; (inclusive)
  </table>

  <p> The &lsquo;<a href="#voice-balance"><code
   class=property>voice-balance</code></a>&rsquo; property controls the
   spatial distribution of audio output across a lateral sound stage: one
   extremity is on the left, the other extremity is on the right hand side,
   relative to the listener's position. Authors can specify intermediary
   steps between left and right extremities, to represent the audio
   separation along the resulting left-right axis.

  <p class=note> Note that the functionality provided by this property has no
   match in the SSML markup language <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>&lt;number&gt;</strong>

   <dd>
    <p>A <a href="#number-def">number</a> between &lsquo;<code
     class=css>-100</code>&rsquo; and &lsquo;<code
     class=css>100</code>&rsquo; (inclusive). Values smaller than
     &lsquo;<code class=css>-100</code>&rsquo; are clamped to &lsquo;<code
     class=css>-100</code>&rsquo;. Values greater than &lsquo;<code
     class=css>100</code>&rsquo; are clamped to &lsquo;<code
     class=css>100</code>&rsquo;. The value &lsquo;<code
     class=css>-100</code>&rsquo; represents the left side, and the value
     &lsquo;<code class=css>100</code>&rsquo; represents the right side. The
     value &lsquo;<code class=css>0</code>&rsquo; represents the center point
     whereby there is no discernible audio separation between left and right
     sides (in a stereo sound system, this corresponds to equal distribution
     of audio signals between left and right speakers).</p>

   <dt> <strong>left</strong>

   <dd>
    <p>Same as &lsquo;<code class=css>-100</code>&rsquo;.</p>

   <dt> <strong>center</strong>

   <dd>
    <p>Same as &lsquo;<code class=css>0</code>&rsquo;.</p>

   <dt> <strong>right</strong>

   <dd>
    <p>Same as &lsquo;<code class=css>100</code>&rsquo;.</p>

   <dt> <strong>leftwards</strong>

   <dd>
    <p>Moves the sound to the left, by subtracting 20 from the inherited
     &lsquo;<a href="#voice-balance"><code
     class=property>voice-balance</code></a>&rsquo; value, and by clamping
     the resulting number to &lsquo;<code class=css>-100</code>&rsquo;.</p>

   <dt> <strong>rightwards</strong>

   <dd>
    <p>Moves the sound to the right, by adding 20 to the inherited &lsquo;<a
     href="#voice-balance"><code
     class=property>voice-balance</code></a>&rsquo; value, and by clamping
     the resulting number to &lsquo;<code class=css>100</code>&rsquo;.</p>
  </dl>

  <p> User agents may be connected to different kinds of sound systems,
   featuring varying audio mixing capabilities. The expected behavior for
   mono, stereo, and surround sound systems is defined as follows:

  <ul>
   <li> When user-agents produce audio via a mono-aural sound system (i.e.
    single-speaker setup), the &lsquo;<a href="#voice-balance"><code
    class=property>voice-balance</code></a>&rsquo; property has no effect.

   <li> When user-agents produce audio through a stereo sound system (e.g.
    two speakers, a pair of headphones), the left-right distribution of audio
    signals can precisely match the authored values for the &lsquo;<a
    href="#voice-balance"><code
    class=property>voice-balance</code></a>&rsquo; property.

   <li> When user-agents are capable of mixing audio signals through more
    than 2 channels (e.g. 5-speakers surround sound system, including a
    dedicated center channel), the physical distribution of audio signals
    resulting from the application of the &lsquo;<a
    href="#voice-balance"><code
    class=property>voice-balance</code></a>&rsquo; property should be
    performed so that the listener perceives sound as if it was coming from a
    basic stereo layout. For example, the center channel as well as the
    left/right speakers may be used altogether in order to emulate the
    behavior of the &lsquo;<code class=property>center</code>&rsquo; value.
  </ul>

  <p> Future revisions of the CSS Speech module may include support for
   three-dimensional audio, which would effectively enable authors to specify
   "azimuth" and "elevation" values. In the future, content authored using
   the current specification may therefore be consumed by user-agents which
   are compliant with the version of CSS Speech that supports
   three-dimensional audio. In order to prepare for this possibility, the
   values enabled by the current &lsquo;<a href="#voice-balance"><code
   class=property>voice-balance</code></a>&rsquo; property are designed to
   remain compatible with "azimuth" angles. More precisely, the mapping
   between the current left-right audio axis (lateral sound stage) and the
   envisioned 360 degrees plane around the listener's position is defined as
   follows:

  <ul>
   <li>The value &lsquo;<code class=css>0</code>&rsquo; maps to zero degrees
    (&lsquo;<code class=property>center</code>&rsquo;). This is in "front" of
    the listener, not from "behind".

   <li>The value &lsquo;<code class=css>-100</code>&rsquo; maps to -40
    degrees (&lsquo;<code class=property>left</code>&rsquo;). Negative angles
    are in the counter-clockwise direction (the audio stage is seen from the
    top).

   <li>The value &lsquo;<code class=css>100</code>&rsquo; maps to 40 degrees
    (&lsquo;<code class=property>right</code>&rsquo;). Positive angles are in
    the clockwise direction (the audio stage is seen from the top).

   <li>Intermediary values on the scale from &lsquo;<code
    class=css>-100</code>&rsquo; to &lsquo;<code class=css>100</code>&rsquo;
    map to the angles between -40 and 40 degrees in a numerically
    linearly-proportional manner. For example, &lsquo;<code
    class=css>-50</code>&rsquo; maps to -20 degrees.
  </ul>

  <p class=note> Note that sound systems may be configured by users in such a
   way that it would interfere with the left-right audio distribution
   specified by document authors. Typically, the various "surround" modes
   available in modern sound systems (including systems based on basic stereo
   speakers) tend to greatly alter the perceived spatial arrangement of audio
   signals. The illusion of a three-dimensional sound stage is often achieved
   using a combination of phase shifting, digital delay, volume control
   (channel mixing), and other techniques. Some users may even configure
   their system to "downgrade" any rendered sound to a single mono channel,
   in which case the effect of the &lsquo;<a href="#voice-balance"><code
   class=property>voice-balance</code></a>&rsquo; property would obviously
   not be perceivable at all. The rendering fidelity of authored content is
   therefore dependent on such user customizations, and the &lsquo;<a
   href="#voice-balance"><code class=property>voice-balance</code></a>&rsquo;
   property merely specifies the desired end-result.

  <p class=note> Note that many speech synthesizers only generate mono sound,
   and therefore do not intrinsically support the &lsquo;<a
   href="#voice-balance"><code class=property>voice-balance</code></a>&rsquo;
   property. The sound distribution along the left-right axis consequently
   occurs at post-synthesis stage (when the speech-enabled user-agent mixes
   the various audio sources authored within the document)

  <h2 id=speaking-props><span class=secno>6. </span>Speaking properties</h2>

  <h3 id=speaking-props-speak><span class=secno>6.1. </span>The &lsquo;<a
   href="#speak"><code class=property>speak</code></a>&rsquo; property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=speak>speak</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>auto | none | normal

    <tr>
     <td> <em>Initial:</em>

     <td>auto

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>The &lsquo;<a href="#speak"><code class=property>speak</code></a>&rsquo;
   property determines whether or not to render text aurally.

  <p class=note> Note that the functionality provided by this property has no
   match in the SSML markup language <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>auto</strong>

   <dd>
    <p>Resolves to a computed value of &lsquo;<code
     class=property>none</code>&rsquo; when <a
     href="#display-def">&lsquo;<code
     class=property>display</code>&rsquo;</a> is &lsquo;<code
     class=property>none</code>&rsquo;, otherwise resolves to a computed
     value of &lsquo;<code class=property>auto</code>&rsquo; which yields a
     used value of &lsquo;<code class=property>normal</code>&rsquo;.</p>

    <p class=note> Note that the &lsquo;<code
     class=property>none</code>&rsquo; value of the <a
     href="#display-def">&lsquo;<code
     class=property>display</code>&rsquo;</a> property cannot be overridden
     by descendants of the selected element, but the &lsquo;<code
     class=property>auto</code>&rsquo; value of &lsquo;<a href="#speak"><code
     class=property>speak</code></a>&rsquo; can however be overridden using
     either of &lsquo;<code class=property>none</code>&rsquo; or &lsquo;<code
     class=property>normal</code>&rsquo;.</p>

   <dt> <strong>none</strong>

   <dd>
    <p> This value causes an element (including pauses, cues, rests and
     actual content) to not be rendered (i.e., the element has no effect in
     the aural dimension).</p>

    <p class=note> Note that any of the descendants of the affected element
     are allowed to override this value, so descendants can actually take
     part in the aural rendering despite using &lsquo;<code
     class=property>none</code>&rsquo; at this level. However, the pauses,
     cues, and rests of the ancestor element remain "deactivated" in the
     aural dimension, and therefore do not contribute to the <a
     href="#collapsing">collapsing of pauses</a> or additive behavior of
     adjoining rests.</p>

   <dt> <strong>normal</strong>

   <dd>
    <p> The element is rendered aurally (regardless of its <a
     href="#display-def">&lsquo;<code
     class=property>display</code>&rsquo;</a> value and the <a
     href="#display-def">&lsquo;<code
     class=property>display</code>&rsquo;</a> and &lsquo;<a
     href="#speak"><code class=property>speak</code></a>&rsquo; values of its
     ancestors).</p>

    <p class=note> Note that using this value can result in the element being
     rendered in the aural dimension even though it would not be rendered on
     the visual canvas.</p>
  </dl>

  <h3 id=speaking-props-speak-as><span class=secno>6.2. </span>The &lsquo;<a
   href="#speak-as"><code class=property>speak-as</code></a>&rsquo; property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=speak-as>speak-as</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>normal | spell-out || digits || [ literal-punctuation |
      no-punctuation ]

    <tr>
     <td> <em>Initial:</em>

     <td>normal

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>The &lsquo;<a href="#speak-as"><code
   class=property>speak-as</code></a>&rsquo; property determines in what
   manner text gets rendered aurally, based upon a basic predefined list of
   possible values.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_say-as"><code>say-as</code>
   element</a> from the SSML markup language <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>, whose values are described in
   the <a href="#SSML-SAYAS"
   rel=biblioentry>[SSML-SAYAS]<!--{{SSML-SAYAS}}--></a> W3C Note.

  <dl>
   <dt> <strong>normal</strong>

   <dd>
    <p>Uses language-dependent pronunciation rules for rendering the
     element's content. For example, punctuation is not spoken as-is, but
     instead rendered naturally as appropriate pauses.</p>

   <dt> <strong>spell-out</strong>

   <dd>
    <p>Spells the text one letter at a time (useful for acronyms and
     abbreviations). In languages where accented characters are rare, it is
     permitted to drop accents in favor of alternative unaccented spellings.
     As as example, in English, the word "r&ocirc;le" can also be written as
     "role". A conforming implementation would thus be able to spell-out
     "r&ocirc;le" as "R O L E".</p>

   <dt> <strong>digits</strong>

   <dd>
    <p>Speak numbers one digit at a time, for instance, "twelve" would be
     spoken as "one two", and "31" as "three one".</p>

    <p class=note>Speech synthesizers are knowledgeable about what is and
     what is not a number. The &lsquo;<a href="#speak-as"><code
     class=property>speak-as</code></a>&rsquo; property enables authors to
     control how the user-agent renders numbers, and may be implemented as a
     preprocessing step before passing the text to the actual speech
     synthesizer.</p>

   <dt> <strong>literal-punctuation</strong>

   <dd>
    <p> Punctuation such as semicolons, braces, and so on is named aloud
     (i.e. spoken literally) rather than rendered naturally as appropriate
     pauses.</p>

   <dt> <strong>no-punctuation</strong>

   <dd>
    <p>Punctuation is not rendered: neither spoken nor rendered as pauses.</p>
  </dl>

  <h2 id=pause-props><span class=secno>7. </span>Pause properties</h2>

  <h3 id=pause-props-pause-before-after><span class=secno>7.1. </span>The
   &lsquo;<a href="#pause-before"><code
   class=property>pause-before</code></a>&rsquo; and &lsquo;<a
   href="#pause-after"><code class=property>pause-after</code></a>&rsquo;
   properties</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=pause-before>pause-before</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;time&gt; | none | x-weak | weak | medium | strong | x-strong

    <tr>
     <td> <em>Initial:</em>

     <td>none

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>&nbsp;

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=pause-after>pause-after</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;time&gt; | none | x-weak | weak | medium | strong | x-strong

    <tr>
     <td> <em>Initial:</em>

     <td>none

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>The &lsquo;<a href="#pause-before"><code
   class=property>pause-before</code></a>&rsquo; and &lsquo;<a
   href="#pause-after"><code class=property>pause-after</code></a>&rsquo;
   properties specify a prosodic boundary (silence with a specific duration)
   that occurs before (or after) the speech synthesis rendition of the
   selected element, or if any &lsquo;<a href="#cue-before"><code
   class=property>cue-before</code></a>&rsquo; (or &lsquo;<a
   href="#cue-after"><code class=property>cue-after</code></a>&rsquo;) is
   specified, before (or after) the cue within the <a
   href="#aural-model">audio "box" model</a>.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_break"><code>break</code>
   element</a> from the SSML markup language <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>&lt;time&gt;</strong>

   <dd>
    <p>Expresses the pause in absolute <a href="#time-def">time</a> units
     (seconds and milliseconds, e.g. "+3s", "250ms"). Only non-negative
     values are allowed.</p>

   <dt> <strong>none</strong>

   <dd>
    <p> Equivalent to 0ms (no prosodic break is produced by the speech
     processor).</p>

   <dt> <strong>x-weak</strong>, <strong>weak</strong>,
    <strong>medium</strong>, <strong>strong</strong>, and
    <strong>x-strong</strong>

   <dd>
    <p> Expresses the pause by the strength of the prosodic break in speech
     output. The exact time is implementation-dependent. The values indicate
     monotonically non-decreasing (conceptually increasing) break strength
     between elements.</p>
  </dl>

  <p class=note> Note that stronger content boundaries are typically
   accompanied by pauses. For example, the breaks between paragraphs are
   typically much more substantial than the breaks between words within a
   sentence.

  <div class=example>
   <p> This example illustrates how the default strengths of prosodic breaks
    for specific elements (which are defined by the user-agent stylesheet)
    can be overridden by authored styles.</p>

   <pre>
p { pause: none } /* pause-before: none; pause-after: none */</pre>
  </div>

  <h3 id=pause-props-pause><span class=secno>7.2. </span>The &lsquo;<a
   href="#pause"><code class=property>pause</code></a>&rsquo; shorthand
   property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=pause>pause</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;&lsquo;<a href="#pause-before"><code
      class=property>pause-before</code></a>&rsquo;&gt; &lt;&lsquo;<a
      href="#pause-after"><code
      class=property>pause-after</code></a>&rsquo;&gt;?

    <tr>
     <td> <em>Initial:</em>

     <td>N/A (see individual properties)

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>N/A (see individual properties)
  </table>

  <p>The &lsquo;<a href="#pause"><code class=property>pause</code></a>&rsquo;
   property is a shorthand property for &lsquo;<a href="#pause-before"><code
   class=property>pause-before</code></a>&rsquo; and &lsquo;<a
   href="#pause-after"><code class=property>pause-after</code></a>&rsquo;. If
   two values are given, the first value is &lsquo;<a
   href="#pause-before"><code class=property>pause-before</code></a>&rsquo;
   and the second is &lsquo;<a href="#pause-after"><code
   class=property>pause-after</code></a>&rsquo;. If only one value is given,
   it applies to both properties.

  <div class=example>
   <p> Examples of property values:</p>

   <pre>
h1 { pause: 20ms; } /* pause-before: 20ms; pause-after: 20ms */
h2 { pause: 30ms 40ms; } /* pause-before: 30ms; pause-after: 40ms */
h3 { pause-after: 10ms; } /* pause-before: <i>unspecified</i>; pause-after: 10ms */</pre>
  </div>

  <h3 id=collapsing><span class=secno>7.3. </span>Collapsing pauses</h3>

  <p> The pause defines the minimum distance of the aural "box" to the aural
   "boxes" before and after it. Adjoining pauses are merged by selecting the
   strongest named break and the longest absolute time interval. For example,
   "strong" is selected when comparing "strong" and "weak", "1s" is selected
   when comparing "1s" and "250ms", and "strong" and "250ms" take effect
   additively when comparing "strong" and "250ms".

  <p>The following pauses are adjoining:

  <ol>
   <li>The &lsquo;<a href="#pause-after"><code
    class=property>pause-after</code></a>&rsquo; of an aural "box" and the
    &lsquo;<a href="#pause-after"><code
    class=property>pause-after</code></a>&rsquo; of its last child, provided
    the former has no &lsquo;<a href="#rest-after"><code
    class=property>rest-after</code></a>&rsquo; and no &lsquo;<a
    href="#cue-after"><code class=property>cue-after</code></a>&rsquo;.

   <li>The &lsquo;<a href="#pause-before"><code
    class=property>pause-before</code></a>&rsquo; of an aural "box" and the
    &lsquo;<a href="#pause-before"><code
    class=property>pause-before</code></a>&rsquo; of its first child,
    provided the former has no &lsquo;<a href="#rest-before"><code
    class=property>rest-before</code></a>&rsquo; and no &lsquo;<a
    href="#cue-before"><code class=property>cue-before</code></a>&rsquo;.

   <li>The &lsquo;<a href="#pause-after"><code
    class=property>pause-after</code></a>&rsquo; of an aural "box" and the
    &lsquo;<a href="#pause-before"><code
    class=property>pause-before</code></a>&rsquo; of its next sibling.

   <li>The &lsquo;<a href="#pause-before"><code
    class=property>pause-before</code></a>&rsquo; and &lsquo;<a
    href="#pause-after"><code class=property>pause-after</code></a>&rsquo; of
    an aural "box", if the the "box" has a &lsquo;<a
    href="#voice-duration"><code
    class=property>voice-duration</code></a>&rsquo; of "0ms" and no &lsquo;<a
    href="#rest-before"><code class=property>rest-before</code></a>&rsquo; or
    &lsquo;<a href="#rest-after"><code
    class=property>rest-after</code></a>&rsquo; and no &lsquo;<a
    href="#cue-before"><code class=property>cue-before</code></a>&rsquo; or
    &lsquo;<a href="#cue-after"><code
    class=property>cue-after</code></a>&rsquo;, or if the the "box" has no
    rendered content at all (see &lsquo;<a href="#speak"><code
    class=property>speak</code></a>&rsquo;).
  </ol>

  <p>A collapsed pause is considered adjoining to another pause if any of its
   component pauses is adjoining to that pause.

  <p class=note> Note that &lsquo;<a href="#pause"><code
   class=property>pause</code></a>&rsquo; has been moved from between the
   element's contents and any &lsquo;<a href="#cue"><code
   class=property>cue</code></a>&rsquo; to outside the &lsquo;<a
   href="#cue"><code class=property>cue</code></a>&rsquo;. This is not
   backwards compatible with the informative CSS2.1 Aural appendix <a
   href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>.

  <h2 id=rest-props><span class=secno>8. </span>Rest properties</h2>

  <h3 id=rest-props-rest-before-after><span class=secno>8.1. </span>The
   &lsquo;<a href="#rest-before"><code
   class=property>rest-before</code></a>&rsquo; and &lsquo;<a
   href="#rest-after"><code class=property>rest-after</code></a>&rsquo;
   properties</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=rest-before>rest-before</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;time&gt; | none | x-weak | weak | medium | strong | x-strong

    <tr>
     <td> <em>Initial:</em>

     <td>none

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>&nbsp;

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=rest-after>rest-after</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;time&gt; | none | x-weak | weak | medium | strong | x-strong

    <tr>
     <td> <em>Initial:</em>

     <td>none

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>The &lsquo;<a href="#rest-before"><code
   class=property>rest-before</code></a>&rsquo; and &lsquo;<a
   href="#rest-after"><code class=property>rest-after</code></a>&rsquo;
   properties specify a prosodic boundary (silence with a specific duration)
   that occurs before (or after) the speech synthesis rendition of an element
   within the <a href="#aural-model">audio "box" model</a>.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_break"><code>break</code>
   element</a> from the SSML markup language <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>&lt;time&gt;</strong>

   <dd>
    <p>Expresses the rest in absolute <a href="#time-def">time</a> units
     (seconds and milliseconds, e.g. "+3s", "250ms"). Only non-negative
     values are allowed.</p>

   <dt> <strong>none</strong>

   <dd>
    <p> Equivalent to 0ms (no prosodic break is produced by the speech
     processor).</p>

   <dt> <strong>x-weak</strong>, <strong>weak</strong>,
    <strong>medium</strong>, <strong>strong</strong>, and
    <strong>x-strong</strong>

   <dd>
    <p> Expresses the rest by the strength of the prosodic break in speech
     output. The exact time is implementation-dependent. The values indicate
     monotonically non-decreasing (conceptually increasing) break strength
     between elements.</p>
  </dl>

  <p>As opposed to <a href="#pause-props">pause properties</a>, the rest is
   inserted between the element's content and any &lsquo;<a
   href="#cue-before"><code class=property>cue-before</code></a>&rsquo; or
   &lsquo;<a href="#cue-after"><code
   class=property>cue-after</code></a>&rsquo; content. Adjoining rests are
   treated additively, and do not collapse.

  <h3 id=rest-props-rest><span class=secno>8.2. </span>The &lsquo;<a
   href="#rest"><code class=property>rest</code></a>&rsquo; shorthand
   property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=rest>rest</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;&lsquo;<a href="#rest-before"><code
      class=property>rest-before</code></a>&rsquo;&gt; &lt;&lsquo;<a
      href="#rest-after"><code
      class=property>rest-after</code></a>&rsquo;&gt;?

    <tr>
     <td> <em>Initial:</em>

     <td>N/A (see individual properties)

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>N/A (see individual properties)
  </table>

  <p>The &lsquo;<a href="#rest"><code class=property>rest</code></a>&rsquo;
   property is a shorthand for &lsquo;<a href="#rest-before"><code
   class=property>rest-before</code></a>&rsquo; and &lsquo;<a
   href="#rest-after"><code class=property>rest-after</code></a>&rsquo;. If
   two values are given, the first value is &lsquo;<a
   href="#rest-before"><code class=property>rest-before</code></a>&rsquo; and
   the second is &lsquo;<a href="#rest-after"><code
   class=property>rest-after</code></a>&rsquo;. If only one value is given,
   it applies to both properties.

  <h2 id=cue-props><span class=secno>9. </span>Cue properties</h2>

  <h3 id=cue-props-cue-before-after><span class=secno>9.1. </span>The
   &lsquo;<a href="#cue-before"><code
   class=property>cue-before</code></a>&rsquo; and &lsquo;<a
   href="#cue-after"><code class=property>cue-after</code></a>&rsquo;
   properties</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=cue-before>cue-before</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;uri&gt; &lt;decibel&gt;? | none

    <tr>
     <td> <em>Initial:</em>

     <td>none

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>&nbsp;

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=cue-after>cue-after</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;uri&gt; &lt;decibel&gt;? | none

    <tr>
     <td> <em>Initial:</em>

     <td>none

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>The &lsquo;<a href="#cue-before"><code
   class=property>cue-before</code></a>&rsquo; and &lsquo;<a
   href="#cue-after"><code class=property>cue-after</code></a>&rsquo;
   properties specify auditory icons (i.e. pre-recorded / pre-generated sound
   clips) to be played before (or after) the selected element within the <a
   href="#aural-model">audio "box" model</a>.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_audio"><code>audio</code>
   element</a> from the SSML markup language <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>&lt;uri&gt;</strong>

   <dd>
    <p>The URI designates an auditory icon resource. When a user agent is not
     able to render the specified auditory icon (e.g. missing file resource,
     or unsupported audio codec), it is recommended to produce an alternative
     cue, such as a bell sound.</p>

   <dt> <strong>none</strong>

   <dd>
    <p>Specifies that no auditory icon is used.</p>

   <dt> <strong>&lt;decibel&gt;</strong>

   <dd>
    <p>A <a href="#number-def">number</a> immediately followed by "dB"
     (decibel unit). This represents a change (positive or negative) relative
     to the computed value of the &lsquo;<a href="#voice-volume"><code
     class=property>voice-volume</code></a>&rsquo; property within the <a
     href="#aural-model">aural "box" model</a> of the selected element.
     Decibels express the ratio of the squares of the new signal amplitude
     (a1) and the current amplitude (a0), as per the following logarithmic
     equation: volume(dB) = 20 log10 (a1 / a0)</p>

    <p> When the &lsquo;<a href="#voice-volume"><code
     class=property>voice-volume</code></a>&rsquo; property is set to
     &lsquo;<code class=property>silent</code>&rsquo;, the audio cue is also
     set to &lsquo;<code class=property>silent</code>&rsquo; (regardless of
     this specified &lt;decibel&gt; value). Otherwise (when not &lsquo;<code
     class=property>silent</code>&rsquo;), &lsquo;<a
     href="#voice-volume"><code class=property>voice-volume</code></a>&rsquo;
     values are always specified relatively to the volume level keywords,
     which map to a user-configured scale of "preferred" loudness settings
     (see the definition of &lsquo;<a href="#voice-volume"><code
     class=property>voice-volume</code></a>&rsquo;). If the inherited
     &lsquo;<a href="#voice-volume"><code
     class=property>voice-volume</code></a>&rsquo; value already contains a
     decibel offset, the dB offset specific to the audio cue is combined
     additively.

    <p> The desired effect of an audio cue set at +0dB is that the volume
     level during playback of the pre-recorded / pre-generated audio signal
     is effectively the same as the loudness of live (i.e. real-time) speech
     synthesis rendition. In order to achieve this effect, speech processors
     are capable of directly controlling the waveform amplitude of generated
     text-to-speech audio, user agents must be able to adjust the volume
     output of audio cues (i.e. amplify or attenuate audio signals based on
     the intrinsic waveform amplitude of digitized sound clips), and last but
     not least, authors must ensure that the "normal" volume level of
     pre-recorded audio cues (on average, as there may be discrete loudness
     variations due to changes in the audio stream, such as intonation,
     stress, etc.) matches that of a "typical" TTS voice output (based on the
     &lsquo;<a href="#voice-family"><code
     class=property>voice-family</code></a>&rsquo; intended for use), given
     standard listening conditions (i.e. default system volume levels,
     centered equalization across the frequency spectrum). This latter
     prerequisite sets a baseline that enables a user agent to align the
     volume outputs of both TTS and cue audio streams within the same aural
     "box" model. Due to the complex relationship between perceived audio
     characteristics and the processing applied to the digitized audio
     signal, we will simplify the definition of "normal" volume levels by
     referring to a canonical recording scenario, whereby the attenuation is
     typically indicated in decibels, ranging from 0dB (maximum audio input,
     near clipping threshold) to -60dB (total silence). In this common
     context, a "standard" audio clip would oscillate between these values,
     the loudest peak levels would be close to -3dB (to avoid distortion),
     and the relevant audible passages would have average (RMS) volume levels
     as high as possible (i.e. not too quiet, to avoid background noise
     during amplification). This would roughly provide an audio experience
     that could be seamlessly combined with text-to-speech output (i.e. there
     would be no discernible difference in volume levels when switching from
     pre-recorded audio to speech synthesis). Although there exists no
     industry-wide standard to support such convention, TTS engines usually
     generate comparably-loud audio signals when no gain or attenuation is
     specified. For voice and soft music, -15dB RMS seems to be pretty
     standard.</p>

    <p class=note> Note that -6.0dB is approximately half the amplitude of
     the audio signal, and +6.0dB is approximately twice the amplitude.</p>

    <p class=note> Note that there is a difference between an audio cue whose
     volume is set to &lsquo;<code class=property>silent</code>&rsquo; and
     one whose value is &lsquo;<code class=property>none</code>&rsquo;. In
     the former case, the audio cue takes up the same time as if it had been
     played, but no sound is generated. In the latter case, the there is no
     manifestation of the audio cue at all (i.e. no time is allocated for the
     cue in the aural dimension).</p>
  </dl>

  <div class=example>
   <p> Examples of property values:</p>

   <pre>
a
{
  cue-before: url(/audio/bell.aiff) -3dB;
  cue-after: url(dong.wav);
}
                
h1
{
  cue-before: url(../clips-1/pop.au) +6dB;
  cue-after: url(../clips-2/pop.au) 6dB;
}

div.caution { cue-before: url(./audio/caution.wav) +8dB; }</pre>
  </div>

  <h3 id=cue-props-cue><span class=secno>9.2. </span>The &lsquo;<a
   href="#cue"><code class=property>cue</code></a>&rsquo; shorthand property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=cue>cue</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;&lsquo;<a href="#cue-before"><code
      class=property>cue-before</code></a>&rsquo;&gt; &lt;&lsquo;<a
      href="#cue-after"><code class=property>cue-after</code></a>&rsquo;&gt;?

    <tr>
     <td> <em>Initial:</em>

     <td>N/A (see individual properties)

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>N/A (see individual properties)
  </table>

  <p>The &lsquo;<a href="#cue"><code class=property>cue</code></a>&rsquo;
   property is a shorthand for &lsquo;<a href="#cue-before"><code
   class=property>cue-before</code></a>&rsquo; and &lsquo;<a
   href="#cue-after"><code class=property>cue-after</code></a>&rsquo;. If two
   values are given the first value is &lsquo;<a href="#cue-before"><code
   class=property>cue-before</code></a>&rsquo; and the second is &lsquo;<a
   href="#cue-after"><code class=property>cue-after</code></a>&rsquo;. If
   only one value is given, it applies to both properties.

  <div class=example>
   <p> Example of shorthand notation:</p>

   <pre>
h1
{
  cue-before: url(pop.au);
  cue-after: url(pop.au);
}
/* ...is equivalent to: */
h1
{
  cue: url(pop.au);
}</pre>
  </div>

  <h2 id=voice-char-props><span class=secno>10. </span>Voice characteristic
   properties</h2>

  <h3 id=voice-props-voice-family><span class=secno>10.1. </span>The
   &lsquo;<a href="#voice-family"><code
   class=property>voice-family</code></a>&rsquo; property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=voice-family>voice-family</dfn>

    <tr>
     <td> <em>Value:</em>

     <td> [[&lt;name&gt; | &lt;generic-voice&gt;],]* [&lt;name&gt; |
      &lt;generic-voice&gt;] | preserve

    <tr>
     <td> <em>Initial:</em>

     <td>implementation-dependent

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>The &lsquo;<a href="#voice-family"><code
   class=property>voice-family</code></a>&rsquo; property specifies a
   prioritized list of component values that are separated by commas to
   indicate that they are alternatives (this is analogous to &lsquo;<code
   class=css><a href="#font-family-def"><code
   class=property>font-family</code></a></code>&rsquo; in visual style
   sheets). Each component value potentially designates a speech synthesis
   voice instance, by specifying match criteria (see the <a
   href="#voice-selection">voice selection</a> section on this topic).

  <p> <strong>&lt;generic-voice&gt;</strong> = [&lt;age&gt;? &lt;gender&gt;
   &lt;integer&gt;?]

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_voice"><code>voice</code>
   element</a> from the SSML markup language <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>&lt;name&gt;</strong>

   <dd>
    <p>Values are specific voice instances (e.g., Mike, comedian, mary,
     carlos2, "valley girl"). Voice names must either be given quoted as <a
     href="#strings-def">strings</a>, or unquoted as a sequence of one or
     more <a href="#identifier-def">identifiers</a>.</p>

    <p class=note>Note that as a result, most punctuation characters, or
     digits at the start of each token, must be escaped in unquoted voice
     names.</p>

    <p> If a sequence of identifiers is given as a voice name, the computed
     value is the name converted to a string by joining all the identifiers
     in the sequence by single spaces.</p>

    <p> Voice names that happen to be the same as the gender keywords
     (&lsquo;<code class=property>male</code>&rsquo;, &lsquo;<code
     class=property>female</code>&rsquo; and &lsquo;<code
     class=property>neutral</code>&rsquo;) or that happen to match the
     keywords &lsquo;<code class=property>inherit</code>&rsquo; or
     &lsquo;<code class=property>preserve</code>&rsquo; must be quoted to
     disambiguate with these keywords. The keywords &lsquo;<code
     class=property>initial</code>&rsquo; and &lsquo;<code
     class=property>default</code>&rsquo; are reserved for future use and
     must also be quoted when used as voice names.</p>

    <p class=note> Note that in <a href="#SSML"
     rel=biblioentry>[SSML]<!--{{!SSML}}--></a>, voice names are
     space-separated and cannot contain whitespace characters.</p>

    <p> It is recommended to quote voice names that contain white space,
     digits, or punctuation characters other than hyphens - even if these
     voice names are valid in unquoted form - in order to improve code
     clarity. For example: <code>voice-family: "john doe", "Henry
     the-8th";</code></p>

   <dt> <strong>&lt;age&gt;</strong>

   <dd>
    <p> Possible values are &lsquo;<code class=property>child</code>&rsquo;,
     &lsquo;<code class=property>young</code>&rsquo; and &lsquo;<code
     class=property>old</code>&rsquo;, indicating the preferred age category
     to match during voice selection. The mapping with <a href="#SSML"
     rel=biblioentry>[SSML]<!--{{!SSML}}--></a> ages is defined as follows:
     &lsquo;<code class=property>child</code>&rsquo; = 6 y/o, &lsquo;<code
     class=property>young</code>&rsquo; = 24 y/o, &lsquo;<code
     class=property>old</code>&rsquo; = 75 y/o (note that more flexible age
     ranges may be used by the processor-dependent voice-matching algorithm).
     </p>

    <p class=note> Note that the interpretation of the relationship between a
     person's age and a recognizable type of voice cannot realistically be
     defined in a universal manner, as it effectively depends on numerous
     criteria (cultural, linguistic, biological, etc.). The values provided
     by this specification therefore represent a simplified model that can be
     reasonably applied to a broad variety of speech contexts, albeit at the
     cost of a certain degree of approximation. Future versions of this
     specification may refine the level of precision of the voice-matching
     algorithm, as speech processor implementations become more standardized.
     </p>

   <dt> <strong>&lt;gender&gt;</strong>

   <dd>
    <p> One of the keywords &lsquo;<code class=property>male</code>&rsquo;,
     &lsquo;<code class=property>female</code>&rsquo;, or &lsquo;<code
     class=property>neutral</code>&rsquo;, specifying a male, female, or
     neutral voice, respectively.</p>

   <dt> <strong>&lt;integer&gt;</strong>

   <dd>
    <p>An <a href="#integer-def">integer</a> indicating the preferred variant
     (e.g. "the second male child voice"). Only positive integers (i.e.
     excluding zero) are allowed. The value "1" refers to the first of all
     matching voices.</p>

   <dt> <strong>preserve</strong>

   <dd>
    <p>Indicates that the &lsquo;<a href="#voice-family"><code
     class=property>voice-family</code></a>&rsquo; value gets inherited and
     used regardless of any potential language change within the content
     markup (see the section below about voice selection and language
     handling). This value behaves as &lsquo;<code
     class=property>inherit</code>&rsquo; when applied to the root element.</p>

    <p class=note> Note that descendants of the selected element
     automatically inherit the &lsquo;<code
     class=property>preserve</code>&rsquo; value, unless it is explicitly
     overridden by other &lsquo;<a href="#voice-family"><code
     class=property>voice-family</code></a>&rsquo; values (e.g. name, gender,
     age).</p>
  </dl>

  <div class=example>
   <p> Examples of invalid declarations:</p>

   <pre>
voice-family: john/doe; /* forward slash character should be escaped */
voice-family: john "doe"; /* identifier sequence cannot contain strings */
voice-family: john!; /* exclamation mark should be escaped */
voice-family: john@doe; /* "at" character should be escaped */
voice-family: #john; /* identifier cannot start with hash character */
voice-family: john 1st; /* identifier cannot start with digit */</pre>
  </div>

  <h4 class=no-toc id=voice-selection><span class=secno>10.1.1. </span>Voice
   selection, content language</h4>

  <p>The &lsquo;<a href="#voice-family"><code
   class=property>voice-family</code></a>&rsquo; property is used to guide
   the selection of the speech synthesis voice instance. As part of this
   selection process, speech-capable user agents must also take into account
   the language of the selected element within the markup content. The
   "name", "gender", "age", and preferred "variant" (index) are voice
   selection hints that get carried down the content hierarchy as the
   &lsquo;<a href="#voice-family"><code
   class=property>voice-family</code></a>&rsquo; property value gets
   inherited by descendant elements. At any point within the content
   structure, the language takes precedence (i.e. has a higher priority) over
   the specified CSS voice characteristics.

  <p> The following list outlines the voice selection algorithm (note that
   the definition of "language" is loose here, in order to cater for
   dialectic variations):

  <ol>
   <li> If only a single voice instance is available for the language of the
    selected content, then this voice must be used, regardless of the
    specified CSS voice characteristics.

   <li> If several voice instances are available for the language of the
    selected content, then the chosen voice is the one that most closely
    matches the specified name, or gender, age, and preferred voice variant.
    The actual definition of "best match" is processor-dependent. For
    example, in a system that only has male and female adult voices
    available, a reasonable match for "voice-family: young male" may well be
    a higher-pitched female voice, as this tone of voice would be close to
    that of a young boy. If no voice instance matches the characteristics
    provided by any of the &lsquo;<a href="#voice-family"><code
    class=property>voice-family</code></a>&rsquo; component values, the first
    available voice instance (amongst those suitable for the language of the
    selected content) must be used.

   <li> If no voice is available for the language of the selected content, it
    is recommended that user-agents let the user know about the lack of
    appropriate TTS voice.
  </ol>

  <p>The speech synthesizer voice must be re-evaluated (i.e. the selection
   process must take place once again) whenever any of the CSS voice
   characteristics change within the content flow. The voice must also be
   re-calculated whenever the content language changes, unless the
   &lsquo;<code class=property>preserve</code>&rsquo; keyword is used (this
   may be useful in cases where embedded foreign language text can be spoken
   using a voice not designed for this language, as demonstrated by the
   example below).

  <p class=note>Note that dynamically computing a voice may lead to
   unexpected lag, so user-agents should try to resolve concrete voice
   instances in the document tree before the playback starts.

  <div class=example>
   <p>Examples of property values:</p>

   <pre>
h1 { voice-family: announcer, old male; }
p.romeo  { voice-family: romeo, young male; }
p.juliet { voice-family: juliet, young female; }
p.mercutio { voice-family: young male; }
p.tybalt { voice-family: young male; }
p.nurse { voice-family: amelie; }

...

&lt;p class="romeo" xml:lang="en-US"&gt;
  The French text below will be spoken with an English voice: 
  &lt;span style="voice-family: preserve;" xml:lang="fr-FR"&gt;Bonjour monsieur !&lt;/span&gt;
  
  The English text below will be spoken with a voice different
  than that corresponding to the class "romeo"
  (which is inherited from the "p" parent element): 
  &lt;span style="voice-family: female;"&gt;Hello sir!&lt;/span&gt;
&lt;/p&gt;</pre>
  </div>

  <h3 id=voice-props-voice-rate><span class=secno>10.2. </span>The &lsquo;<a
   href="#voice-rate"><code class=property>voice-rate</code></a>&rsquo;
   property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=voice-rate>voice-rate</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>[normal | x-slow | slow | medium | fast | x-fast] ||
      &lt;percentage&gt;

    <tr>
     <td> <em>Initial:</em>

     <td>normal

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>refer to default value

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>a keyword value, and optionally also a percentage relative to the
      keyword (if not 100%)
  </table>

  <p>The &lsquo;<a href="#voice-rate"><code
   class=property>voice-rate</code></a>&rsquo; property manipulates the rate
   of generated synthetic speech in terms of words per minute.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_prosody"><code>rate</code>
   attribute of the <code>prosody</code> element</a> from the SSML markup
   language <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>normal</strong>

   <dd>
    <p>Represents the default rate produced by the speech synthesizer for the
     currently active voice. This is processor-specific and depends on the
     language, dialect and on the "personality" of the voice.</p>

   <dt><strong>x-slow</strong>, <strong>slow</strong>,
    <strong>medium</strong>, <strong>fast</strong> and
    <strong>x-fast</strong>

   <dd>
    <p>A sequence of monotonically non-decreasing speaking rates that are
     implementation and voice -specific. For example, typical values for the
     English language are (in words per minute) x-slow = 80, slow = 120,
     medium = between 180 and 200, fast = 500.</p>

   <dt> <strong>&lt;percentage&gt;</strong>

   <dd>
    <p>Only non-negative <a href="#percentage-def">percentage</a> values are
     allowed. This represents a change relative to the given keyword value
     (see enumeration above), or to the default value for the root element,
     or otherwise to the inherited speaking rate (which may itself be a
     combination of a keyword value and of a percentage, in which case
     percentages are combined multiplicatively). For example, 50% means that
     the speaking rate gets multiplied by 0.5 (half the value).</p>
  </dl>

  <div class=example>
   <p>Examples of inherited values:</p>

   <pre>
&lt;body&gt;
  &lt;e1&gt;
    &lt;e2&gt;
      &lt;e3&gt;
        ...
      &lt;/e3&gt;
    &lt;/e2&gt;
  &lt;/e1&gt;
&lt;/body&gt;




body { voice-rate: inherit; } /* the initial value is 'normal'
                               (the actual speaking rate value
                               depends on the active voice) */

e1 { voice-rate: +50%; } /* the computed value is
                          ['normal' and 50%], which will resolve
                          to the rate corresponding to 'normal'
                          multiplied by 0.5 (half the speaking rate) */

e2 { voice-rate: fast 120%; } /* the computed value is
                          ['fast' and 120%], which will resolve
                          to the rate corresponding to 'fast'
                          multiplied by 1.2 (one and a half times the speaking rate) */
                          
e3 { voice-rate: normal; /* "resets" the speaking rate to the intrinsic voice value,
                            the computed value is 'normal' (see comment below for actual value) */
                           
     voice-family: "another-voice"; } /* because the voice is different,
                                      the calculated speaking rate may vary
                                      compared to "body" (even though the computed
                                      'voice-rate' value is the same) */
      </pre>
  </div>

  <h3 id=voice-props-voice-pitch><span class=secno>10.3. </span>The &lsquo;<a
   href="#voice-pitch"><code class=property>voice-pitch</code></a>&rsquo;
   property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=voice-pitch>voice-pitch</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;frequency&gt; &amp;&amp; absolute | [[x-low | low | medium |
      high | x-high] || [&lt;frequency&gt; | &lt;semitones&gt; |
      &lt;percentage&gt;]]

    <tr>
     <td> <em>Initial:</em>

     <td>medium

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>refer to inherited value

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td> one of the predefined pitch keywords if only the keyword is
      specified by itself, otherwise an absolute frequency calculated by
      converting the keyword value (if any) to a fixed frequency based on the
      current voice-family and by applying the specified relative offset (if
      any)
  </table>

  <p>The &lsquo;<a href="#voice-pitch"><code
   class=property>voice-pitch</code></a>&rsquo; property specifies the
   "baseline" pitch of the generated speech output, which depends on the used
   &lsquo;<a href="#voice-family"><code
   class=property>voice-family</code></a>&rsquo; instance, and varies across
   speech synthesis processors (it approximately corresponds to the average
   pitch of the output). For example, the common pitch for a male voice is
   around 120Hz, whereas it is around 210Hz for a female voice.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_prosody"><code>pitch</code>
   attribute of the <code>prosody</code> element</a> from the SSML markup
   language <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>&lt;frequency&gt;</strong>

   <dd>
    <p> A value in <a href="#frequency-def">frequency</a> units (Hertz or
     kiloHertz, e.g. "100Hz", "+2kHz"). Values are restricted to positive
     numbers when the &lsquo;<code class=property>absolute</code>&rsquo;
     keyword is specified. Otherwise (when the &lsquo;<code
     class=property>absolute</code>&rsquo; keyword is not specified), a
     negative value represents a decrement, and a positive value represents
     an increment, relative to the inherited value. For example, "2kHz" is a
     positive offset (strictly equivalent to "+2kHz"), and "+2kHz absolute"
     is an absolute frequency (strictly equivalent to "2kHz absolute").</p>

   <dt> <strong>absolute</strong>

   <dd>
    <p> If specified, this keyword indicates that the specified frequency
     represents an absolute value. If a negative frequency is specified, the
     computed frequency will be zero.</p>

   <dt> <strong>&lt;semitones&gt;</strong>

   <dd>
    <p> Specifies a relative change (decrement or increment) to the inherited
     value. The syntax of allowed values is a &lt;<a
     href="#number-def">number</a>&gt; followed immediately by "st"
     (semitones). A semitone interval corresponds to the step between each
     note on an equal temperament chromatic scale. A semitone can therefore
     be quantified as the difference between two consecutive pitch
     frequencies on such scale. The ratio between two consecutive frequencies
     separated by exactly one semitone is the twelfth root of two
     (approximately 11011/10393, which equals exactly 1.0594631). As a
     result, the value in Hertz corresponding to a semitone offset is
     relative to the initial frequency the offset is applied to (in other
     words, a semitone doesn't correspond to a fixed numerical value in
     Hertz).</p>

   <dt> <strong>&lt;percentage&gt;</strong>

   <dd>
    <p> Positive and negative <a href="#percentage-def">percentage</a> values
     are allowed, to represent an increment or decrement (respectively)
     relative to the inherited value. Computed values are calculated by
     adding (or subtracting) the specified fraction of the inherited value,
     to (from) the inherited value. For example, 50% (which is equivalent to
     +50%) with a inherited value of 200Hz results in <code>200 +
     (200*0.5)</code> = 300Hz. Conversely, -50% results in
     <code>200-(200*0.5)</code> = 100Hz.</p>

   <dt><strong>x-low</strong>, <strong>low</strong>, <strong>medium</strong>,
    <strong>high</strong>, <strong>x-high</strong>

   <dd>
    <p>A sequence of monotonically non-decreasing pitch levels that are
     implementation and voice specific. When the computed value for a given
     element is only a keyword (i.e. no relative offset is specified), then
     the corresponding absolute frequency will be re-evaluated on a voice
     change. Conversely, the application of a relative offset requires the
     calculation of the resulting frequency based on the current voice at the
     point at which the relative offset is specified, so the computed
     frequency will inherit absolutely regardless of any voice change further
     down the style cascade. Authors should therefore only use keyword values
     in cases where they wish that voice changes trigger the re-evaluation of
     the conversion from a keyword to a concrete, voice-dependent frequency.</p>
  </dl>

  <p> Computed absolute frequencies that are negative are clamped to zero
   Hertz. Speech-capable user agents are likely to support a specific range
   of values rather than the full range of possible calculated numerical
   values for frequencies. The actual values in user agents may therefore be
   clamped to implementation-dependent minimum and maximum boundaries. For
   example: although the 0Hz frequency can be legitimately calculated, it may
   be clamped to a more meaningful value in the context of the speech
   synthesizer.

  <div class=example>
   <p>Examples of property values:</p>

   <pre>
h1 { voice-pitch: 250Hz; } /* positive offset relative to the inherited absolute frequency */
h1 { voice-pitch: +250Hz; } /* identical to the line above */
h2 { voice-pitch: +30Hz absolute; } /* not an increment */
h2 { voice-pitch: absolute 30Hz; } /* identical to the line above */
h3 { voice-pitch: -20Hz; } /* negative offset (decrement) relative to the inherited absolute frequency */
h4 { voice-pitch: -20Hz absolute; } /* illegal syntax => value ignored ("absolute" keyword not allowed with negative frequency) */
h5 { voice-pitch: -3.5st; } /* semitones, negative offset */
h6 { voice-pitch: 25%; } /* this means "add a quarter of the inherited value, to the inherited value" */
h6 { voice-pitch: +25%; } /* identical to the line above */
      </pre>
  </div>

  <h3 id=voice-props-voice-range><span class=secno>10.4. </span>The &lsquo;<a
   href="#voice-range"><code class=property>voice-range</code></a>&rsquo;
   property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=voice-range>voice-range</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>&lt;frequency&gt; &amp;&amp; absolute | [[x-low | low | medium |
      high | x-high] || [&lt;frequency&gt; | &lt;semitones&gt; |
      &lt;percentage&gt;]]

    <tr>
     <td> <em>Initial:</em>

     <td>medium

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>refer to inherited value

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td> one of the predefined pitch keywords if only the keyword is
      specified by itself, otherwise an absolute frequency calculated by
      converting the keyword value (if any) to a fixed frequency based on the
      current voice-family and by applying the specified relative offset (if
      any)
  </table>

  <p> The &lsquo;<a href="#voice-range"><code
   class=property>voice-range</code></a>&rsquo; property specifies the
   variability in the "baseline" pitch, i.e. how much the fundamental
   frequency may deviate from the average pitch of the speech output. The
   dynamic pitch range of the generated speech generally increases for a
   highly animated voice, for example when variations in inflection are used
   to convey meaning and emphasis in speech. Typically, a low range produces
   a flat, monotonic voice, whereas a high range produces an animated voice.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_prosody"><code>range</code>
   attribute of the <code>prosody</code> element</a> from the SSML markup
   language <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>&lt;frequency&gt;</strong>

   <dd>
    <p> A value in <a href="#frequency-def">frequency</a> units (Hertz or
     kiloHertz, e.g. "100Hz", "+2kHz"). Values are restricted to positive
     numbers when the &lsquo;<code class=property>absolute</code>&rsquo;
     keyword is specified. Otherwise (when the &lsquo;<code
     class=property>absolute</code>&rsquo; keyword is not specified), a
     negative value represents a decrement, and a positive value represents
     an increment, relative to the inherited value. For example, "2kHz" is a
     positive offset (strictly equivalent to "+2kHz"), and "+2kHz absolute"
     is an absolute frequency (strictly equivalent to "2kHz absolute").</p>

   <dt> <strong>absolute</strong>

   <dd>
    <p> If specified, this keyword indicates that the specified frequency
     represents an absolute value. If a negative frequency is specified, the
     computed frequency will be zero.</p>

   <dt> <strong>&lt;semitones&gt;</strong>

   <dd>
    <p> Specifies a relative change (decrement or increment) to the inherited
     value. The syntax of allowed values is a &lt;<a
     href="#number-def">number</a>&gt; followed immediately by "st"
     (semitones). A semitone interval corresponds to the step between each
     note on an equal temperament chromatic scale. A semitone can therefore
     be quantified as the difference between two consecutive pitch
     frequencies on such scale. The ratio between two consecutive frequencies
     separated by exactly one semitone is the twelfth root of two
     (approximately 11011/10393, which equals exactly 1.0594631). As a
     result, the value in Hertz corresponding to a semitone offset is
     relative to the initial frequency the offset is applied to (in other
     words, a semitone doesn't correspond to a fixed numerical value in
     Hertz).</p>

   <dt> <strong>&lt;percentage&gt;</strong>

   <dd>
    <p> Positive and negative <a href="#percentage-def">percentage</a> values
     are allowed, to represent an increment or decrement (respectively)
     relative to the inherited value. Computed values are calculated by
     adding (or subtracting) the specified fraction of the inherited value,
     to (from) the inherited value. For example, 50% (which is equivalent to
     +50%) with a inherited value of 200Hz results in <code>200 +
     (200*0.5)</code> = 300Hz. Conversely, -50% results in
     <code>200-(200*0.5)</code> = 100Hz.</p>

   <dt><strong>x-low</strong>, <strong>low</strong>, <strong>medium</strong>,
    <strong>high</strong>, <strong>x-high</strong>

   <dd>
    <p>A sequence of monotonically non-decreasing pitch levels that are
     implementation and voice specific. When the computed value for a given
     element is only a keyword (i.e. no relative offset is specified), then
     the corresponding absolute frequency will be re-evaluated on a voice
     change. Conversely, the application of a relative offset requires the
     calculation of the resulting frequency based on the current voice at the
     point at which the relative offset is specified, so the computed
     frequency will inherit absolutely regardless of any voice change further
     down the style cascade. Authors should therefore only use keyword values
     in cases where they wish that voice changes trigger the re-evaluation of
     the conversion from a keyword to a concrete, voice-dependent frequency.</p>
  </dl>

  <p> Computed absolute frequencies that are negative are clamped to zero
   Hertz. Speech-capable user agents are likely to support a specific range
   of values rather than the full range of possible calculated numerical
   values for frequencies. The actual values in user agents may therefore be
   clamped to implementation-dependent minimum and maximum boundaries. For
   example: although the 0Hz frequency can be legitimately calculated, it may
   be clamped to a more meaningful value in the context of the speech
   synthesizer.

  <div class=example>
   <p>Examples of inherited values:</p>

   <pre>
&lt;body&gt;
  &lt;e1&gt;
    &lt;e2&gt;
      &lt;e3&gt;
        &lt;e4&gt;
          &lt;e5&gt;
            &lt;e6&gt;
            ...
            &lt;/e6&gt;
          &lt;/e5&gt;
        &lt;/e4&gt;
      &lt;/e3&gt;
    &lt;/e2&gt;
  &lt;/e1&gt;
&lt;/body&gt;




body { voice-range: inherit; } /* the initial value is 'medium'
                               (the actual frequency value
                               depends on the current voice) */

e1 { voice-range: +25%; } /* the computed value is
                          ['medium' + 25%] which resolves
                          to the frequency corresponding to 'medium'
                          plus 0.25 times the frequency
                          corresponding to 'medium' */

e2 { voice-range: +10Hz; } /* the computed value is
                          [FREQ + 10Hz] where "FREQ" is the absolute frequency
                          calculated in the "e1" rule above.
                          */
                          
e3 { voice-range: inherit; /* this could be omitted,
                           but we explicitly specify it for clarity purposes */
                           
     voice-family: "another-voice"; } /* this voice change would have resulted in
                              the re-evaluation of the initial 'medium' keyword
                              inherited by the "body" element
                              (i.e. conversion from a voice-dependent keyword value
                              to a concrete, absolute frequency),
                              but because relative offsets were applied down the style
                              cascade, the inherited value is actually the frequency
                              calculated at the "e2" rule above. */

e4 { voice-range: 200Hz absolute; } /* override with an absolute frequency
                                    which doesn't depend on the current voice */

e5 { voice-range: 2st; } /* the computed value is an absolute frequency,
                         which is the result of the
                         calculation: 200Hz + two semitones
                         (reminder: the actual frequency corresponding to a semitone
                         depends on the base value to which it applies) */

e6 { voice-range: inherit; /* this could be omitted,
                           but we explicitly specify it for clarity purposes */
                           
     voice-family: "yet-another-voice"; } /* despite the voice change,
                              the computed value is the same as
                              for "e5" (i.e. an absolute frequency value,
                              independent from the current voice) */
      </pre>
  </div>

  <h3 id=voice-props-voice-stress><span class=secno>10.5. </span>The
   &lsquo;<a href="#voice-stress"><code
   class=property>voice-stress</code></a>&rsquo; property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=voice-stress>voice-stress</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>normal | strong | moderate | none | reduced

    <tr>
     <td> <em>Initial:</em>

     <td>normal

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>yes

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p>The &lsquo;<a href="#voice-stress"><code
   class=property>voice-stress</code></a>&rsquo; property manipulates the
   strength of emphasis, which is normally applied using a combination of
   pitch change, timing changes, loudness and other acoustic differences. The
   precise meaning of the values therefore depend on the language being
   spoken.

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_emphasis"><code>emphasis</code>
   element</a> from the SSML markup language <a href="#SSML"
   rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>normal</strong>

   <dd>
    <p>Represents the default emphasis produced by the speech synthesizer.</p>

   <dt> <strong>none</strong>

   <dd>
    <p>Prevents the synthesizer from emphasizing text it would normally
     emphasize.</p>

   <dt><strong>moderate</strong> and <strong>strong</strong>

   <dd>
    <p>These values are monotonically non-decreasing in strength. Their
     application results in more emphasis than what the speech synthesizer
     would normally produce (i.e. more than the value corresponding to
     &lsquo;<code class=property>normal</code>&rsquo;).</p>

   <dt> <strong>reduced</strong>

   <dd>
    <p>Effectively the opposite of emphasizing a word.</p>
  </dl>

  <div class=example>
   <p>Examples of property values, with HTML sample:</p>

   <pre>
span.default-emphasis { voice-stress: normal; }
span.lowered-emphasis { voice-stress: reduced; }
span.removed-emphasis { voice-stress: none; }
span.normal-emphasis { voice-stress: moderate; }
span.huge-emphasis { voice-stress: strong; }
                
...

&lt;p&gt;This is a big car.&lt;/p&gt;
&lt;!-- The speech output from the line above is identical to the line below: --&gt;
&lt;p&gt;This is a &lt;span class="default-emphasis"&gt;big&lt;/span&gt; car.&lt;/p&gt;

&lt;p&gt;This car is &lt;span class="lowered-emphasis"&gt;massive&lt;/span&gt;!&lt;/p&gt;
&lt;!-- The "span" below is totally de-emphasized, whereas the emphasis in the line above is only reduced: --&gt;
&lt;p&gt;This car is &lt;span class="removed-emphasis"&gt;massive&lt;/span&gt;!&lt;/p&gt;

&lt;!-- The lines below demonstrate increasing levels of emphasis: --&gt;
&lt;p&gt;This is a &lt;span class="normal-emphasis"&gt;big&lt;/span&gt; car!&lt;/p&gt;
&lt;p&gt;This is a &lt;span class="huge-emphasis"&gt;big&lt;/span&gt; car!!!&lt;/p&gt;</pre>
  </div>

  <h2 id=duration-props><span class=secno>11. </span>Voice duration property</h2>

  <h3 id=mixing-props-voice-duration><span class=secno>11.1. </span>The
   &lsquo;<a href="#voice-duration"><code
   class=property>voice-duration</code></a>&rsquo; property</h3>

  <table class=propdef summary="name: syntax">
   <tbody>
    <tr>
     <td>Name:

     <td> <dfn id=voice-duration>voice-duration</dfn>

    <tr>
     <td> <em>Value:</em>

     <td>auto | &lt;time&gt;

    <tr>
     <td> <em>Initial:</em>

     <td> <em>auto</em>

    <tr>
     <td> <em>Applies&nbsp;to:</em>

     <td>all elements

    <tr>
     <td> <em>Inherited:</em>

     <td>no

    <tr>
     <td> <em>Percentages:</em>

     <td>N/A

    <tr>
     <td> <em>Media:</em>

     <td>speech

    <tr>
     <td> <em>Computed value:</em>

     <td>specified value
  </table>

  <p> The &lsquo;<a href="#voice-duration"><code
   class=property>voice-duration</code></a>&rsquo; property specifies how
   long it should take to render the selected element's content (not
   including <a href="#cue-props">audio cues</a>, <a href="#pause-props">
   pauses</a> and <a href="#rest-props">rests</a> ). Unless the value
   &lsquo;<code class=property>auto</code>&rsquo; is specified, this property
   takes precedence over the &lsquo;<a href="#voice-rate"><code
   class=property>voice-rate</code></a>&rsquo; property, and should be used
   to determine a suitable speaking rate for the voice. An element for which
   the &lsquo;<a href="#voice-duration"><code
   class=property>voice-duration</code></a>&rsquo; property value is not
   &lsquo;<code class=property>auto</code>&rsquo; may have descendants for
   which the &lsquo;<a href="#voice-duration"><code
   class=property>voice-duration</code></a>&rsquo; and &lsquo;<a
   href="#voice-rate"><code class=property>voice-rate</code></a>&rsquo;
   properties are specified, but these must be ignored. In other words, when
   a &lsquo;<code class=property>time</code>&rsquo; is specified for the
   &lsquo;<a href="#voice-duration"><code
   class=property>voice-duration</code></a>&rsquo; of a selected element, it
   applies to the entire element subtree (children cannot override the
   property).

  <p class=note> Note that the functionality provided by this property is
   related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_prosody"><code>duration</code>
   attribute of the <code>prosody</code> element</a> from the SSML markup
   language <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <dl>
   <dt> <strong>auto</strong>

   <dd>
    <p>Resolves to a used value corresponding to the duration of the speech
     synthesis when using the inherited &lsquo;<a href="#voice-rate"><code
     class=property>voice-rate</code></a>&rsquo;.</p>

   <dt> <strong>&lt;time&gt;</strong>

   <dd>
    <p> Specifies a value in absolute <a href="#time-def">time</a> units
     (seconds and milliseconds, e.g. "+3s", "250ms"). Only non-negative
     values are allowed.</p>
  </dl>

  <h2 id=lists><span class=secno>12. </span>List items and counters styles</h2>

  <p>The &lsquo;<code class=css><a href="#list-style-type-def"> <code
   class=property>list-style-type</code></a></code>&rsquo; property of <a
   href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> specifies three
   types of list item markers: glyphs, numbering systems, and alphabetic
   systems. The values allowed for this property are also used for the
   counter() function of the &lsquo;<a href="#content-def"><code
   class=property>content</code></a>&rsquo; property. The CSS Speech module
   defines how to render these styles in the aural dimension, using speech
   synthesis. The &lsquo;<code class=css><a
   href="#list-style-image-def"><code
   class=property>list-style-image</code></a></code>&rsquo; property of <a
   href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> is ignored, and
   instead the &lsquo;<code class=css><a href="#list-style-type-def"><code
   class=property>list-style-type</code></a></code>&rsquo; is used.

  <p class=note> Note that the speech rendering of new features from the CSS
   Lists and Counters Module Level 3 <a href="#CSS3LIST"
   rel=biblioentry>[CSS3LIST]<!--{{CSS3LIST}}--></a> is not covered in this
   level of CSS Speech, but may be defined in a future specification.

  <dl>
   <dt> <strong>disc, circle, square</strong>

   <dd>
    <p> For these list item styles, the user-agent defines (possibly based on
     user preferences) what equivalent phrase is spoken or what audio cue is
     played. List items with graphical bullets are therefore announced
     appropriately in an implementation-dependent manner.</p>

   <dt> <strong>decimal, decimal-leading-zero, lower-roman, upper-roman,
    georgian, armenian</strong>

   <dd>
    <p> For these list item styles, corresponding numbers are spoken as-is by
     the speech synthesizer, and may be complemented with additional audio
     cues or speech phrases in the document's language (i.e. with the same
     TTS voice used to speak the list item content) in order to indicate the
     presence of list items. For example, when using the English language,
     the list item counter could be prefixed with the word "Item", which
     would result in list items being announced with "Item one", "Item two",
     etc.</p>

   <dt> <strong>lower-latin, lower-alpha, upper-latin, upper-alpha,
    lower-greek</strong>

   <dd>
    <p> These list item styles are spelled out letter-by-letter by the speech
     synthesizer, in the document language (i.e. with the same TTS voice used
     to speak the list item content). For example, &lsquo;<code
     class=property>lower-greek</code>&rsquo; in English would be read out as
     "alpha", "beta", "gamma", etc. Conversely, &lsquo;<code
     class=property>upper-latin</code>&rsquo; in French would be read out as
     /a/, /be/, /se/, etc. (phonetic notation)</p>
  </dl>

  <p class=note>Note that it is common for user-agents such as screen readers
   to announce the nesting depth of list items, or more generally, to
   indicate additional structural information pertaining to complex
   hierarchical content. The verbosity of these additional audio cues and/or
   speech output can usually be controlled by users, and contribute to
   increasing usability. These navigation aids are implementation-dependent,
   but it is recommended that user-agents supporting the CSS Speech module
   ensure that these additional audio cues and speech output don't generate
   redundancies or create inconsistencies (for example: duplicated or
   different list item numbering scheme).

  <h2 id=content><span class=secno>13. </span>Inserted and replaced content</h2>

  <p class=note>Note that this entire section is non-normative.

  <p>Sometimes, authors will want to specify a mapping from the source text
   into another string prior to the application of the regular pronunciation
   rules. This may be used for uncommon abbreviations or acronyms which are
   unlikely to be recognized by the synthesizer. The &lsquo;<a
   href="#content-def"><code class=property>content</code></a>&rsquo;
   property can be used to replace one string by another. The functionality
   provided by this property is related to the <a
   href="http://www.w3.org/TR/speech-synthesis11/#edef_sub"><code>alias</code>
   attribute of the <code>sub</code> element</a> from the SSML markup
   language <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>.

  <div class=example>
   <p> In this example, the abbreviation is rendered using the content of the
    title attribute instead of the element's content.</p>

   <pre>
/* This replaces the content of the selected element
by the string "World Wide Web Consortium". */
abbr { content: attr(title); }
...

&lt;abbr title="World Wide Web Consortium"&gt;W3C&lt;/abbr&gt;</pre>
  </div>

  <p>In a similar way, text strings in a document can be replaced by a
   previously recorded version.

  <div class=example>
   <p>In this example - assuming the format is supported, the file is
    available and the UA is configured to do so - a recording of Sir John
    Gielgud's declamation of the famous monologue is played. Otherwise the UA
    falls back to render the text using synthesized speech.</p>

   <pre>
.hamlet { content: url(./audio/gielgud.wav); }
...

&lt;div class="hamlet"&gt;
To be, or not to be: that is the question:
&lt;/div&gt;</pre>
  </div>

  <p>Furthermore, authors (or users via a user stylesheet) may add some
   information to ease the understanding of structures during non-visual
   interaction with the document. They can do so by using the &lsquo;<code
   class=css>::before</code>&rsquo; and &lsquo;<code
   class=css>::after</code>&rsquo; pseudo-elements. Note that different
   stylesheets can be used to define the level of verbosity for additional
   information spoken by screen readers.

  <div class=example>
   <p>This example inserts the string "Start list: " before a list and the
    string "List item: " before the content of each list item. Likewise, the
    string "List end: " gets inserted after the list to inform the user that
    the list speech output is over.</p>

   <pre>
ul::before { content: "Start list: "; }
ul::after  { content: "List end. "; }
li::before { content: "List item: "; }</pre>
  </div>

  <p>Detailed information can be found in the CSS3 Generated and Replaced
   Content module <a href="#CSS3GENCON"
   rel=biblioentry>[CSS3GENCON]<!--{{CSS3GENCON}}--></a>.

  <h2 id=pronunciation><span class=secno>14. </span> Pronunciation, phonemes</h2>

  <p class=note>Note that this entire section is non-normative.

  <p> CSS does not specify how to define the pronunciation (expressed using a
   well-defined phonetic alphabet) of a particular piece of text within the
   markup document. A "phonemes" property was described in earlier drafts of
   this specification, but objections were raised due to breaking the
   principle of separation between content and presentation (the "phonemes"
   authored within aural CSS stylesheets would have needed to be updated each
   time text changed within the markup document). The "phonemes"
   functionality is therefore considered out-of-scope in CSS (the
   presentation layer) and should be addressed in the markup / content layer.

  <p> The <a
   href="http://microformats.org/wiki/rel-pronunciation">"pronunciation"</a>
   <code>rel</code> value allows importing pronunciation lexicons in HTML
   documents using the <code>link</code> element (similar to how CSS
   stylesheets can be included). The W3C PLS (Pronunciation Lexicon
   Specification) <a href="#PRONUNCIATION-LEXICON"
   rel=biblioentry>[PRONUNCIATION-LEXICON]<!--{{PRONUNCIATION-LEXICON}}--></a>
   is one format that can be used to describe such a lexicon.

  <p> Additionally, an attribute-based mechanism can be used within the
   markup to author text-pronunciation associations. At the time of writing,
   such mechanism isn't formally defined in the W3C HTML standard(s).
   However, the <a href="http://idpf.org/epub/30">EPUB 3.0 draft
   specification</a> allows (x)HTML5 documents to contain attributes derived
   from the <a href="#SSML" rel=biblioentry>[SSML]<!--{{!SSML}}--></a>
   specification, that describe how to pronounce text based on a particular
   phonetic alphabet.</p>
  <!-- p> 
      One avenue to explore is the use CSS to "bind" HTML text with a   
      phoneme (also declared in the HTML document). This would maintain a   
      clear separation between content and presentation, and it would allow   
      authors to define different pronunciations for one given text token   
      (Media Queries could drive the switch of stylesheet to import). This   
      possibility has been mentioned several times by Working Group members   
      as well as people from the public mailing-list, so it cannot be   
      ignored. However, there are architectural considerations (e.g.   
      collision between CSS versus HTML -defined phonemes) which make this a   
      lot trickier to standardize than it sounds. The   
      whole "speech synthesis" issue should be tackled globally at the level   
      of the W3C ecosystem. For example, there are many cross-cutting   
      concerns with the work done by the HTML-Audio and HTML-Speech   
      Incubator Groups.
      </p -->

  <h2 class=no-num id=property-index>Appendix A &mdash; Property index</h2>
  <!--begin-properties-->

  <table class=proptable>
   <thead>
    <tr>
     <th>Property

     <th>Values

     <th>Initial

     <th>Applies&nbsp;to

     <th>Inh.

     <th>Percentages

     <th>Media

   <tbody>
    <tr>
     <th><a class=property href="#cue">cue</a>

     <td>&lt;&lsquo;cue-before&rsquo;&gt; &lt;&lsquo;cue-after&rsquo;&gt;?

     <td>N/A (see individual properties)

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#cue-after">cue-after</a>

     <td>&lt;uri&gt; &lt;decibel&gt;? | none

     <td>none

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#cue-before">cue-before</a>

     <td>&lt;uri&gt; &lt;decibel&gt;? | none

     <td>none

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#pause">pause</a>

     <td>&lt;&lsquo;pause-before&rsquo;&gt;
      &lt;&lsquo;pause-after&rsquo;&gt;?

     <td>N/A (see individual properties)

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#pause-after">pause-after</a>

     <td>&lt;time&gt; | none | x-weak | weak | medium | strong | x-strong

     <td>none

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#pause-before">pause-before</a>

     <td>&lt;time&gt; | none | x-weak | weak | medium | strong | x-strong

     <td>none

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#rest">rest</a>

     <td>&lt;&lsquo;rest-before&rsquo;&gt; &lt;&lsquo;rest-after&rsquo;&gt;?

     <td>N/A (see individual properties)

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#rest-after">rest-after</a>

     <td>&lt;time&gt; | none | x-weak | weak | medium | strong | x-strong

     <td>none

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#rest-before">rest-before</a>

     <td>&lt;time&gt; | none | x-weak | weak | medium | strong | x-strong

     <td>none

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#speak">speak</a>

     <td>auto | none | normal

     <td>auto

     <td>all elements

     <td>yes

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#speak-as">speak-as</a>

     <td>normal | spell-out || digits || [ literal-punctuation |
      no-punctuation ]

     <td>normal

     <td>all elements

     <td>yes

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#voice-balance">voice-balance</a>

     <td>&lt;number&gt; | left | center | right | leftwards | rightwards

     <td>center

     <td>all elements

     <td>yes

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#voice-duration">voice-duration</a>

     <td>auto | &lt;time&gt;

     <td>auto

     <td>all elements

     <td>no

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#voice-family">voice-family</a>

     <td>[[&lt;name&gt; | &lt;generic-voice&gt;],]* [&lt;name&gt; |
      &lt;generic-voice&gt;] | preserve

     <td>implementation-dependent

     <td>all elements

     <td>yes

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#voice-pitch">voice-pitch</a>

     <td>&lt;frequency&gt; &amp;&amp; absolute | [[x-low | low | medium |
      high | x-high] || [&lt;frequency&gt; | &lt;semitones&gt; |
      &lt;percentage&gt;]]

     <td>medium

     <td>all elements

     <td>yes

     <td>refer to inherited value

     <td>speech

    <tr>
     <th><a class=property href="#voice-range">voice-range</a>

     <td>&lt;frequency&gt; &amp;&amp; absolute | [[x-low | low | medium |
      high | x-high] || [&lt;frequency&gt; | &lt;semitones&gt; |
      &lt;percentage&gt;]]

     <td>medium

     <td>all elements

     <td>yes

     <td>refer to inherited value

     <td>speech

    <tr>
     <th><a class=property href="#voice-rate">voice-rate</a>

     <td>[normal | x-slow | slow | medium | fast | x-fast] ||
      &lt;percentage&gt;

     <td>normal

     <td>all elements

     <td>yes

     <td>refer to default value

     <td>speech

    <tr>
     <th><a class=property href="#voice-stress">voice-stress</a>

     <td>normal | strong | moderate | none | reduced

     <td>normal

     <td>all elements

     <td>yes

     <td>N/A

     <td>speech

    <tr>
     <th><a class=property href="#voice-volume">voice-volume</a>

     <td>silent | [[x-soft | soft | medium | loud | x-loud] ||
      &lt;decibel&gt;]

     <td>medium

     <td>all elements

     <td>yes

     <td>N/A

     <td>speech
  </table>
  <!--end-properties-->

  <p>The following properties are defined in other modules or specifications:

  <ul>
   <li> <dfn id=display-def> <a
    href="http://www.w3.org/TR/CSS21/visuren.html#display-prop"> display
    </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li> <dfn id=padding-def> <a
    href="http://www.w3.org/TR/CSS21/box.html#padding-properties"> padding
    </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li> <dfn id=border-def> <a
    href="http://www.w3.org/TR/CSS21/box.html#border-properties"> border
    </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li> <dfn id=margin-def> <a
    href="http://www.w3.org/TR/CSS21/box.html#margin-properties"> margin
    </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li> <dfn id=font-family-def> <a
    href="http://www.w3.org/TR/CSS21/fonts.html#font-family-prop">
    font-family </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li><dfn id=content-def>content</dfn> &nbsp;&nbsp; <a href="#CSS3GENCON"
    rel=biblioentry>[CSS3GENCON]<!--{{CSS3GENCON}}--></a>

   <li> <dfn id=list-style-type-def> <a
    href="http://www.w3.org/TR/CSS21/generate.html#propdef-list-style-type">
    list-style-type </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li> <dfn id=list-style-image-def> <a
    href="http://www.w3.org/TR/CSS21/generate.html#propdef-list-style-image">
    list-style-image </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>
  </ul>

  <p>The following definitions are provided by other modules or
   specifications:

  <ul>
   <li> <dfn id=cascade-def> <a
    href="http://www.w3.org/TR/CSS21/cascade.html#cascade"> cascade
    </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li> <dfn id=box-model-def> <a href="http://www.w3.org/TR/CSS21/box.html">
    visual box model </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li> <dfn id=time-def> <a href="http://www.w3.org/TR/css3-values/#times">
    time </a></dfn> &nbsp;&nbsp; <a href="#CSS3VAL"
    rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>

   <li> <dfn id=frequency-def> <a
    href="http://www.w3.org/TR/css3-values/#frequencies"> frequency
    </a></dfn> &nbsp;&nbsp; <a href="#CSS3VAL"
    rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>

   <li> <dfn id=number-def> <a
    href="http://www.w3.org/TR/css3-values/#ltnumbergt"> number </a></dfn>
    &nbsp;&nbsp; <a href="#CSS3VAL"
    rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>

   <li> <dfn id=integer-def> <a
    href="http://www.w3.org/TR/css3-values/#ltintegergt"> integer </a></dfn>
    &nbsp;&nbsp; <a href="#CSS3VAL"
    rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>

   <li> <dfn id=non-negative-number-def> <a
    href="http://www.w3.org/TR/css3-values/#non-negative">
    non-negative-number </a></dfn> &nbsp;&nbsp; <a href="#CSS3VAL"
    rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>

   <li> <dfn id=percentage-def> <a
    href="http://www.w3.org/TR/css3-values/#percentages"> percentage
    </a></dfn> &nbsp;&nbsp; <a href="#CSS3VAL"
    rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>

   <li> <dfn id=identifier-def> <a
    href="http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier">
    identifier </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>

   <li> <dfn id=strings-def> <a
    href="http://www.w3.org/TR/CSS21/syndata.html#strings"> strings
    </a></dfn> &nbsp;&nbsp; <a href="#CSS21"
    rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>
  </ul>

  <h2 class=no-num id=index>Appendix B &mdash; Index</h2>
  <!--begin-index-->

  <ul class=indexlist>
   <li>aural "box" model, <a href="#aural-box-model" title="aural
    &quot;box&quot; model"><strong>4.</strong></a>

   <li>authoring tool, <a href="#authoring-tool" title="authoring
    tool"><strong>#</strong></a>

   <li>border, <a href="#border-def" title=border><strong>#</strong></a>

   <li>cascade, <a href="#cascade-def" title=cascade><strong>#</strong></a>

   <li>content, <a href="#content-def" title=content><strong>#</strong></a>

   <li>cue, <a href="#cue" title=cue><strong>9.2.</strong></a>

   <li>cue-after, <a href="#cue-after"
    title=cue-after><strong>9.1.</strong></a>

   <li>cue-before, <a href="#cue-before"
    title=cue-before><strong>9.1.</strong></a>

   <li>display, <a href="#display-def" title=display><strong>#</strong></a>

   <li>document, <a href="#document" title=document><strong>#</strong></a>

   <li>documents, <a href="#document" title=documents><strong>#</strong></a>

   <li>font-family, <a href="#font-family-def"
    title=font-family><strong>#</strong></a>

   <li>frequency, <a href="#frequency-def"
    title=frequency><strong>#</strong></a>

   <li>identifier, <a href="#identifier-def"
    title=identifier><strong>#</strong></a>

   <li>integer, <a href="#integer-def" title=integer><strong>#</strong></a>

   <li>list-style-image, <a href="#list-style-image-def"
    title=list-style-image><strong>#</strong></a>

   <li>list-style-type, <a href="#list-style-type-def"
    title=list-style-type><strong>#</strong></a>

   <li>margin, <a href="#margin-def" title=margin><strong>#</strong></a>

   <li>non-negative-number, <a href="#non-negative-number-def"
    title=non-negative-number><strong>#</strong></a>

   <li>number, <a href="#number-def" title=number><strong>#</strong></a>

   <li>padding, <a href="#padding-def" title=padding><strong>#</strong></a>

   <li>pause, <a href="#pause" title=pause><strong>7.2.</strong></a>

   <li>pause-after, <a href="#pause-after"
    title=pause-after><strong>7.1.</strong></a>

   <li>pause-before, <a href="#pause-before"
    title=pause-before><strong>7.1.</strong></a>

   <li>percentage, <a href="#percentage-def"
    title=percentage><strong>#</strong></a>

   <li>renderer, <a href="#renderer" title=renderer><strong>#</strong></a>

   <li>rest, <a href="#rest" title=rest><strong>8.2.</strong></a>

   <li>rest-after, <a href="#rest-after"
    title=rest-after><strong>8.1.</strong></a>

   <li>rest-before, <a href="#rest-before"
    title=rest-before><strong>8.1.</strong></a>

   <li>speak, <a href="#speak" title=speak><strong>6.1.</strong></a>

   <li>speak-as, <a href="#speak-as" title=speak-as><strong>6.2.</strong></a>
    

   <li>strings, <a href="#strings-def" title=strings><strong>#</strong></a>

   <li>style sheet, <a href="#style-sheet" title="style
    sheet"><strong>#</strong></a>
    <ul>
     <li>as conformance class, <a href="#style-sheet0" title="style sheet, as
      conformance class"><strong>#</strong></a>
    </ul>

   <li>time, <a href="#time-def" title=time><strong>#</strong></a>

   <li>UA, <a href="#ua" title=UA><strong>#</strong></a>

   <li>User Agent, <a href="#user-agent" title="User
    Agent"><strong>#</strong></a>

   <li>visual box model, <a href="#box-model-def" title="visual box
    model"><strong>#</strong></a>

   <li>voice-balance, <a href="#voice-balance"
    title=voice-balance><strong>5.2.</strong></a>

   <li>voice-duration, <a href="#voice-duration"
    title=voice-duration><strong>11.1.</strong></a>

   <li>voice-family, <a href="#voice-family"
    title=voice-family><strong>10.1.</strong></a>

   <li>voice-pitch, <a href="#voice-pitch"
    title=voice-pitch><strong>10.3.</strong></a>

   <li>voice-range, <a href="#voice-range"
    title=voice-range><strong>10.4.</strong></a>

   <li>voice-rate, <a href="#voice-rate"
    title=voice-rate><strong>10.2.</strong></a>

   <li>voice-stress, <a href="#voice-stress"
    title=voice-stress><strong>10.5.</strong></a>

   <li>voice-volume, <a href="#voice-volume"
    title=voice-volume><strong>5.1.</strong></a>
  </ul>
  <!--end-index-->

  <h2 class=no-num id=definitions>Appendix C &mdash; Definitions</h2>

  <h3 class=no-num id=glossary>Glossary</h3>

  <p>The following terms and abbreviations are used in this module.

  <dl>
   <dt> <dfn id=ua>UA</dfn>

   <dt> <dfn id=user-agent>User Agent</dfn>

   <dd>
    <p>A program that reads and/or writes CSS style sheets on behalf of a
     user in either or both of these categories: programs whose purpose is to
     render <a href="#document">documents</a> (e.g., browsers) and programs
     whose purpose is to create style sheets (e.g., editors). A UA may fall
     into both categories. (There are other programs that read or write style
     sheets, but this module gives no rules for them.)</p>

   <dt> <dfn id=document title="document|documents">document</dfn>

   <dd>
    <p>A tree-structured document with elements and attributes, such as an
     SGML or XML document <a href="#XML11"
     rel=biblioentry>[XML11]<!--{{!XML11}}--></a>.</p>

   <dt> <dfn id=style-sheet>style sheet</dfn>

   <dd>
    <p>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
     style sheet</a></p>
  </dl>

  <h3 class=no-num id=conformance>Conformance</h3>

  <p>Conformance requirements are expressed with a combination of descriptive
   assertions and RFC 2119 terminology. The key words "MUST", "MUST NOT",
   "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
   "MAY", and "OPTIONAL" in the normative parts of this document are to be
   interpreted as described in RFC 2119. However, for readability, these
   words do not appear in all uppercase letters in this specification. All of
   the text of this specification is normative except sections explicitly
   marked as non-normative, examples, and notes. <a href="#RFC2119"
   rel=biblioentry>[RFC2119]<!--{{!RFC2119}}--></a>

  <p>Examples in this specification are introduced with the words "for
   example" or are set apart from the normative text with
   <code>class="example"</code>, like this:

  <div class=example>
   <p>This is an example of an informative example.</p>
  </div>

  <p>Informative notes begin with the word "Note" and are set apart from the
   normative text with <code>class="note"</code>, like this:

  <p class=note>Note, this is an informative note.

  <p>Conformance to the CSS3 Speech module is defined for three classes:

  <dl>
   <dt> <dfn id=style-sheet0 title="style sheet!!as conformance class">style
    sheet</dfn>

   <dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
    style sheet</a>.

   <dt> <dfn id=renderer>renderer</dfn>

   <dd>A UA that interprets the semantics of a style sheet and renders <a
    href="#document">documents</a> that use them.

   <dt> <dfn id=authoring-tool>authoring tool</dfn>

   <dd>A UA that writes a style sheet.
  </dl>

  <p>A style sheet is conformant to the CSS3 Speech module if all of its
   declarations that use properties defined in this module have values that
   are valid according to the generic CSS grammar and the individual grammars
   of each property as given in this module.

  <p>A renderer is conformant to the CSS3 Speech module if, in addition to
   interpreting the style sheet as defined by the appropriate specifications,
   it supports all the properties defined by CSS3 Speech module by parsing
   them correctly and rendering the document accordingly. However the
   inability of a UA to correctly render a document due to limitations of the
   device does not make the UA non-conformant. (For example, a UA is not
   required to render color on a monochrome monitor.)

  <p>An authoring tool is conformant to CSS3 Speech module if it writes
   syntactically correct style sheets, according to the generic CSS grammar
   and the individual grammars of each property in this module.</p>
  <!-- h3 class="no-num" id="levels">Levels</h3>
            
            <p><em>This section is informative.</em> CSS has different levels of
            features, each a subset of the other. (See [[CSSBEIJING]] for a full
            explanation.) The lists below describe which features from this
            specification are in each level.
            
            <h4 class="no-num" id="level-1">CSS Level 1</h4>
            <ul>
            <li>'background-color'
            <li>'background-image' only one image (no layers)
            <li>'background-repeat': only 'repeat' | 'repeat-x' | 'repeat-y' | 'no-repeat'
            <li>'background-attachment': only 'scroll' | 'fixed'
            <li>'background-position': only one or two values allowed
            <li>'background' shorthand: only color, image, repeat, attachment and position
            <li>'border-color' properties
            <li>'border-style' properties
            <li>'border-width' properties
            <li>'border-top', 'border-bottom', 'border-right', 'border-left', and 'border' shorthands
            </ul>
            
            <h4 class="no-num" id="level-2">CSS Level 2</h4>
            <ul>
            <li>'background-color'
            <li>'background-image': only one image (no layers)
            <li>'background-repeat': only 'repeat' | 'repeat-x' | 'repeat-y' | 'no-repeat'
            <li>'background-attachment': only 'scroll' | 'fixed'
            <li>'background-position': only one or two values allowed
            <li>'background': only color, image, repeat, attachment and position
            <li>'border-color' properties
            <li>'border-style' properties
            <li>'border-width' properties
            <li>'border-top', 'border-bottom', 'border-right', 'border-left', and 'border' shorthands
            </ul>
            
            <h4 class="no-num" id="level-3">CSS Level 3</h4>
            <ul>
            <li>All features described in the CSS3 Speech module
            </ul -->

  <h3 class=no-num id=exit>CR exit criteria</h3>

  <p>As described in the W3C process document, a <a
   href="http://www.w3.org/2005/10/Process-20051014/tr.html#cfi">Candidate
   Recommendation</a> (CR) is a specification that W3C recommends for use on
   the Web. The next stage is "Recommendation" when the specification is
   sufficiently implemented.

  <p>For this specification to be proposed as a W3C Recommendation, the
   following conditions shall be met. There must be at least two independent,
   interoperable implementations of each feature. Each feature may be
   implemented by a different set of products, there is no requirement that
   all features be implemented by a single product. For the purposes of this
   criterion, we define the following terms:

  <dl>
   <dt>independent

   <dd>each implementation must be developed by a different party and cannot
    share, reuse, or derive from code used by another qualifying
    implementation. Sections of code that have no bearing on the
    implementation of this specification are exempt from this requirement.

   <dt>interoperable

   <dd>passing the respective test case(s) in the official CSS test suite,
    or, if the implementation is not a Web browser, an equivalent test. Every
    relevant test in the test suite should have an equivalent test created if
    such a user agent (UA) is to be used to claim interoperability. In
    addition if such a UA is to be used to claim interoperability, then there
    must one or more additional UAs which can also pass those equivalent
    tests in the same way for the purpose of interoperability. The equivalent
    tests must be made publicly available for the purposes of peer review.

   <dt>implementation

   <dd>a user agent which:
    <ol class=inline>
     <li>implements the specification.

     <li>is available to the general public. The implementation may be a
      shipping product or other publicly available version (i.e., beta
      version, preview release, or "nightly build"). Non-shipping product
      releases must have implemented the feature(s) for a period of at least
      one month in order to demonstrate stability.

     <li>is not experimental (i.e., a version specifically designed to pass
      the test suite and is not intended for normal usage going forward).
    </ol>
  </dl>

  <p>A minimum of sixth months of the CR period must have elapsed. This is to
   ensure that enough time is given for any remaining major errors to be
   caught.

  <p>Features will be dropped if two or more interoperable implementations
   are not found by the end of the CR period.

  <p>Features may/will also be dropped if adequate/sufficient (by judgment of
   CSS WG) tests have not been produced for those feature(s) by the end of
   the CR period.

  <h2 class=no-num id=ack>Appendix D &mdash; Acknowledgements</h2>

  <p>The editors would like to thank the members of the W3C Voice Browser and
   Cascading Style Sheets working groups for their assistance in preparing
   this specification. Special thanks to Ellen Eide (IBM) for her detailed
   comments, and to Elika Etemad (Fantasai) for her thorough reviews.

  <h2 class=no-num id=changes>Appendix E &mdash; Changes from previous draft</h2>

  <p> Note that the <a
   href="http://www.w3.org/TR/2011/WD-css3-speech-20110419">previous Working
   Draft</a> includes <a
   href="http://www.w3.org/TR/2011/WD-css3-speech-20110419#changes">its own
   list of changes</a>, which - for succinctness - is not repeated here.

  <ul>
   <li>Renamed &lsquo;<code class=property>voice-pitch-range</code>&rsquo; to
    &lsquo;<a href="#voice-range"><code
    class=property>voice-range</code></a>&rsquo;, which is compatible with
    SSML's notation, and removes the possibility to interpret this property
    as being a subset of &lsquo;<a href="#voice-pitch"><code
    class=property>voice-pitch</code></a>&rsquo;.

   <li>Fixed "computed value" for &lsquo;<a href="#voice-pitch"><code
    class=property>voice-pitch</code></a>&rsquo; and &lsquo;<a
    href="#voice-range"><code class=property>voice-range</code></a>&rsquo;
    properties, and added the possibility to combine a keyword with a
    relative change.

   <li>Removed the "phonemes" property (and its associated "@alphabet"
    at-rule).

   <li>Renamed &lsquo;<code class=property>speakability</code>&rsquo; to
    &lsquo;<a href="#speak"><code class=property>speak</code></a>&rsquo;, and
    &lsquo;<a href="#speak"><code class=property>speak</code></a>&rsquo; to
    &lsquo;<a href="#speak-as"><code
    class=property>speak-as</code></a>&rsquo;. Reorganized the &lsquo;<a
    href="#speak-as"><code class=property>speak-as</code></a>&rsquo; values
    to allow mixing different types.

   <li>Added support for lists and counters (item styles, numbering, etc.).

   <li>Adjusted the [initial] value for shorthand properties, to be
    consistent with other CSS specifications (i.e. "see individual
    properties"), and removed the erroneous "inherit" value.

   <li>Fixed &lsquo;<a href="#voice-volume"><code
    class=property>voice-volume</code></a>&rsquo; by conforming to SSML 1.1
    (dB scale, etc.).

   <li>Fixed the [initial] values for &lsquo;<a href="#pause"><code
    class=property>pause</code></a>&rsquo; and &lsquo;<a href="#rest"><code
    class=property>rest</code></a>&rsquo;, which should be zero (were
    "implementation-dependent").

   <li>Corrected the [initial] values for &lsquo;<a href="#voice-range"><code
    class=property>voice-range</code></a>&rsquo; and &lsquo;<a
    href="#voice-pitch"><code class=property>voice-pitch</code></a>&rsquo; to
    "medium".

   <li>Added an "auto" value to &lsquo;<a href="#voice-duration"><code
    class=property>voice-duration</code></a>&rsquo;, which is the [initial]
    property value as well.

   <li>Handling of &lsquo;<a href="#voice-balance"><code
    class=property>voice-balance</code></a>&rsquo; values outside of the
    allowed range (clamping).

   <li>Fixed &lsquo;<a href="#voice-balance"><code
    class=property>voice-balance</code></a>&rsquo; prose to better explain
    the relationship between author intent (stereo sound distribution) and
    actual user sound system setup (mono, stereo, or surround speaker layout
    / mixing capabilities).

   <li>Added prose for &lsquo;<a href="#voice-balance"><code
    class=property>voice-balance</code></a>&rsquo; to describe the mapping
    between stereo left-right sound axis and three-dimensional sound stage
    (azimuth support in future versions of CSS-Speech).

   <li>Fixed the "computed value" for &lsquo;<a href="#voice-balance"><code
    class=property>voice-balance</code></a>&rsquo;.

   <li>Added the &lsquo;<code class=property>normal</code>&rsquo; value for
    voice-rate ("default" in SSML 1.1).

   <li>Fixed the "computed value" for voice-rate, and added the possibility
    to combine keywords and percentages (to be consistent with &lsquo;<a
    href="#voice-volume"><code
    class=property>voice-volume</code></a>&rsquo;). Added an example to
    illustrate inheritance and value resolution.

   <li>Renamed voice-family fields to be consistent with SSML.

   <li>Improved the &lsquo;<a href="#voice-family"><code
    class=property>voice-family</code></a>&rsquo; selection algorithm to
    cater for language changes.

   <li>Separated definition of semitones (pitch properties).

   <li>More consistent behavior when audio cue URI fails (for whatever
    reason).

   <li>Enabled voice-family names to contain spaces, matching &lsquo;<code
    class=property>font-family</code>&rsquo; syntax which is based on quoted
    strings and concatenated identifiers.

   <li>Added a new section to define the relationship of this specification
    with CSS2.1.

   <li>Added the missing "Computed value" line to each property definition.

   <li>Cleaned-up the list of module dependencies, and removed redundant
    "module dependencies" section.

   <li> Voice age keywords now mapped to SSML ages.

   <li>Improved the pause collapsing prose, removed redundant paragraphs.

   <li>Added the missing &lsquo;<code class=property>normal</code>&rsquo;
    value for &lsquo;<a href="#voice-stress"><code
    class=property>voice-stress</code></a>&rsquo;.

   <li>Separated the &lsquo;<code class=property>absolute</code>&rsquo;
    keyword for &lsquo;<a href="#voice-pitch"><code
    class=property>voice-pitch</code></a>&rsquo; and &lsquo;<a
    href="#voice-range"><code class=property>voice-range</code></a>&rsquo;.

   <li>Improved document structure by adding sub-sections.

   <li>Removed the implicit &lsquo;<code class=property>inherit</code>&rsquo;
    value for all properties.

   <li>Fixed typos and made other minor edits.
  </ul>
  <!-- For reference only, changes in previous draft: -->
  <!-- ul>
            <li>Removed the "mark" property, see the <a href="http://lists.w3.org/Archives/Public/www-style/2011Feb/0029.html">Working Group resolution</a></li>
            <li>Added the 'speakability' property and removed the 'none' value of the 'speak' property,
            as per this <a href="http://lists.w3.org/Archives/Public/www-style/2011Jan/0483.html">discussion</a></li>
            <li>Fixed 'voice-family' grammar as per <a href="http://lists.w3.org/Archives/Public/www-style/2010Dec/0231.html">this discussion</a></li>
            <li>The volume level of audio cues can only be set relatively to the inherited 'voice-volume' property (to avoid cues being spoken when the main element is silent, which contradicts the "aural box model").</li>
            <li>Added "HTML" to "CSS defines aural properties that give control over rendering
            XML to speech" in the abstract.</li>
            <li>Removed unused normative links to CSS3 modules (actually moved to informative references), now the only dependency is CSS3 Values and Units.</li>
            <li>Removed issue about the 'sub' SSML element given that the CSS "content" replacement functionality addresses the same requirement.</li>
            <li>Added support for semitones in pitch alterations.</li>
            <li>Added reference to "time" values syntax (s, ms) for 'voice-duration'.</li>
            <li>Moved "content" outside of "phonetics", as the ::before and ::after use-cases do not relate to pronunciation rules (this is actually more similar to audio cues, only applied with text rather than audio files)</li>
            <li>Added prose to explicitly support alphabet other than IPA, via the "x-" vendor-specific prefix.</li>
            <li>Reworked HTML source code to work with the <a href="http://cgi.w3.org/member-bin/process.cgi">members-only W3C pre-processor/generator</a></li>
            <li>Added note about the "speech" and "aural" media types.</li>
            <li>Harmonized all hyperlinks so that CSS properties get auto-linked by the pre-processor</li>
            <li>Clarified computation rules for positive percentages with "+" prefixes (i.e. they do not denote increments, the regular multiplicative behavior is used).</li>
            <li>Fixed IPA URL reference</li>
            <li>Reorganized appendixes</li>
            <li>Fixed minor typos</li>
            </ul -->

  <h2 class=no-num id=references>Appendix F &mdash; References</h2>

  <h3 class=no-num id=normative-references>Normative references</h3>
  <!--begin-normative-->
  <!-- Sorted by label -->

  <dl class=bibliography>
   <dt style="display: none"><!-- keeps the doc valid if the DL is empty -->
    <!---->

   <dt id=CSS21>[CSS21]

   <dd>Bert Bos; et al. <a
    href="http://www.w3.org/TR/2011/REC-CSS2-20110607"><cite>Cascading Style
    Sheets Level 2 Revision 1 (CSS&#160;2.1) Specification.</cite></a> 7 June
    2011. W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/2011/REC-CSS2-20110607">http://www.w3.org/TR/2011/REC-CSS2-20110607</a>
    </dd>
   <!---->

   <dt id=CSS3VAL>[CSS3VAL]

   <dd>H&#229;kon Wium Lie; Chris Lilley. <a
    href="http://www.w3.org/TR/2006/WD-css3-values-20060919"><cite>CSS3
    Values and Units.</cite></a> 19 September 2006. W3C Working Draft. (Work
    in progress.) URL: <a
    href="http://www.w3.org/TR/2006/WD-css3-values-20060919">http://www.w3.org/TR/2006/WD-css3-values-20060919</a>
    </dd>
   <!---->

   <dt id=RFC2119>[RFC2119]

   <dd>S. Bradner. <a href="http://www.ietf.org/rfc/rfc2119.txt"><cite>Key
    words for use in RFCs to Indicate Requirement Levels.</cite></a> Internet
    RFC 2119. URL: <a
    href="http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a>
    </dd>
   <!---->

   <dt id=SSML>[SSML]

   <dd>Daniel C. Burnett; &#21452;&#24535;&#20255; (Zhi Wei Shuang). <a
    href="http://www.w3.org/TR/2010/REC-speech-synthesis11-20100907/"><cite>Speech
    Synthesis Markup Language (SSML) Version 1.1.</cite></a> 7 September
    2010. W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/2010/REC-speech-synthesis11-20100907/">http://www.w3.org/TR/2010/REC-speech-synthesis11-20100907/</a>
    </dd>
   <!---->

   <dt id=XML11>[XML11]

   <dd>Eve Maler; et al. <a
    href="http://www.w3.org/TR/2006/REC-xml11-20060816"><cite>Extensible
    Markup Language (XML) 1.1 (Second Edition).</cite></a> 16 August 2006.
    W3C Recommendation. URL: <a
    href="http://www.w3.org/TR/2006/REC-xml11-20060816">http://www.w3.org/TR/2006/REC-xml11-20060816</a>
    </dd>
   <!---->
  </dl>
  <!--end-normative-->

  <h3 class=no-num id=other-references>Other references</h3>
  <!--begin-informative-->
  <!-- Sorted by label -->

  <dl class=bibliography>
   <dt style="display: none"><!-- keeps the doc valid if the DL is empty -->
    <!---->

   <dt id=CSS3GENCON>[CSS3GENCON]

   <dd>Ian Hickson. <a
    href="http://www.w3.org/TR/2003/WD-css3-content-20030514"><cite>CSS3
    Generated and Replaced Content Module.</cite></a> 14 May 2003. W3C
    Working Draft. (Work in progress.) URL: <a
    href="http://www.w3.org/TR/2003/WD-css3-content-20030514">http://www.w3.org/TR/2003/WD-css3-content-20030514</a>
    </dd>
   <!---->

   <dt id=CSS3LIST>[CSS3LIST]

   <dd>Tab Atkins Jr. <a
    href="http://www.w3.org/TR/2011/WD-css3-lists-20110524"><cite>CSS Lists
    and Counters Module Level 3.</cite></a> 24 May 2011. W3C Working Draft.
    (Work in progress.) URL: <a
    href="http://www.w3.org/TR/2011/WD-css3-lists-20110524">http://www.w3.org/TR/2011/WD-css3-lists-20110524</a>
    </dd>
   <!---->

   <dt id=PRONUNCIATION-LEXICON>[PRONUNCIATION-LEXICON]

   <dd>Paolo Baggia. <a
    href="http://www.w3.org/TR/2008/REC-pronunciation-lexicon-20081014/"><cite>Pronunciation
    Lexicon Specification (PLS) Version 1.0.</cite></a> 14 October 2008. W3C
    Recommendation. URL: <a
    href="http://www.w3.org/TR/2008/REC-pronunciation-lexicon-20081014/">http://www.w3.org/TR/2008/REC-pronunciation-lexicon-20081014/</a>
    </dd>
   <!---->

   <dt id=SSML-SAYAS>[SSML-SAYAS]

   <dd>Daniel C. Burnett; et al. <a
    href="http://www.w3.org/TR/2005/NOTE-ssml-sayas-20050526"><cite>SSML 1.0
    say-as attribute values.</cite></a> 26 May 2005. W3C Working Group Note.
    URL: <a
    href="http://www.w3.org/TR/2005/NOTE-ssml-sayas-20050526">http://www.w3.org/TR/2005/NOTE-ssml-sayas-20050526</a>
    </dd>
   <!---->
  </dl>
  <!--end-informative-->
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