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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 + 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 rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-WD.css" -->
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED" rel="stylesheet" type="text/css" />
</head>
<body>
<div class="head">
<!--logo-->
<h1 id="top">CSS Speech Module</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:</dt>
<dd>
<!--<a href="http://www.w3.org/TR/[YEAR]/WD-[SHORTNAME]-[CDATE]">[VERSION]</a>-->
<a href="http://dev.w3.org/csswg/css3-speech">http://dev.w3.org/csswg/css3-speech</a>
</dd>
<dt>Latest version:</dt>
<dd>
<a href="http://www.w3.org/TR/css3-speech">[LATEST]</a>
</dd>
<dt>Previous versions:</dt>
<dd>
<a href="http://www.w3.org/TR/2004/WD-css3-speech-20041216/"
>http://www.w3.org/TR/2004/WD-css3-speech-20041216/</a>
</dd>
<dt id="editors-list">Editors:</dt>
<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>
<dd><a href="mailto:daniel@glazman.org">Daniel Glazman</a> (<a
href="http://www.disruptive-innovations.com/">Disruptive Innovations</a>)</dd>
<dd><a href="mailto:csant@opera.com">Claudio Santambrogio</a> (<a
href="http://www.opera.com/">Opera Software</a>)</dd>
<dd><a href="mailto:dweck@daisy.org">Daniel Weck</a> (<a href="http://www.daisy.org">DAISY
Consortium</a>)</dd>
</dl>
<!--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 [[!SPEECH-SYNTHESIS]]. Note that this standard was developed in cooperation
with the <a href="http://www.w3.org/Voice/">Voice Browser Activity</a>.</p>
<h2 class="no-num no-toc" id="status">Status of this document</h2>
<!--status-->
<p> </p>
<hr />
<div class="issue">
<p>The following issues need to be discussed and require working group resolutions:</p>
<ul>
<li>
<a href="#issue-lists">handling of list styles, numbered items</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 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.</p>
<hr />
<h2 class="no-num no-toc" id="contents">Table of contents</h2>
<!--toc-->
<hr />
<h2 id="introduction">Introduction</h2>
<p class="note">Note that this entire section is non-normative.</p>
<h3 id="design-goals">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>
<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, volume levels, etc.). These style sheet properties can be used
together with visual properties (mixed media), or as a complete aural alternative to visual
presentation. The aural "canvas" consists of a two-channel (stereo) space and of a temporal
dimension, within which synthetic speech and audio cues coexist.</p>
<h3 id="css21-rel">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 [[!CSS21]] 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. </p>
<p> Note that 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 speech synthesis. </p>
<h3 id="example">CSS Speech Example</h3>
<p>The following 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 (prerecorded 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>
<div class="example">
<pre>
h1, h2, h3, h4, h5, h6
{
voice-family: paul;
voice-stress: moderate;
cue-before: url(../audio/ping.wav);
}
p.heidi
{
voice-family: female;
voice-balance: left;
voice-pitch: high;
}
p.peter
{
voice-family: male;
voice-balance: right;
voice-rate: fast;
}
span.special
{
voice-volume: soft;
pause-after: strong;
}
...
<h1>I am Paul, and I speak headings.</h1>
<p class="heidi">Hello, I am Heidi.</p>
<p class="peter">
<span class="special">Can you hear me ?</span>
I am Peter.
</p>
</pre>
</div>
<h2 id="aural-model">The <dfn id="aural-box-model">aural "box" model</dfn></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 aural "box" model. The aural canvas is one-dimensional, or "monolinear". The
element is surrounded by 'rest', 'cue' and 'pause' properties (from the innermost to the
outermost position). These can be seen as aural equivalents to 'padding', 'border' and
'margin', respectively. The following diagram illustrates the equivalence between properties
of the visual and aural box models, applied to the selected <element>:</p>
<p>
<img alt="A graph depicting the aural 'box' model." id="aural-box" src="aural-box.png" />
</p>
<h2 id="mixing-props">Mixing properties</h2>
<h3 id="mixing-props-voice-volume">The 'voice-volume' property</h3>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="voice-volume">voice-volume</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td>silent | [[ x-soft | soft | medium | loud | x-loud ] && linear ] | [
<non-negative number> && linear ] | <percentage> | inherit</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>medium</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>yes</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>refer to inherited value</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>The 'voice-volume' property manipulates the amplitude of the audio waveform generated by the
speech synthesiser, and is also used to calculate the relative volume level of <a
href="#cue-props">audio cues</a> within the <a href="#aural-model">audio "box" model</a>. </p>
<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 [[!SPEECH-SYNTHESIS]]. </p>
<dl>
<dt>
<strong>silent</strong>
</dt>
<dd>
<p> Specifies that the volume level results in no sound output at all. </p>
<p class="note"> Note that there is a difference between an element whose 'voice-volume'
property has a value of 'silent', and an element whose 'speak' property has the value
'none'. The former takes up the same time as if it had been spoken, including any pause
before and after the element, but no sound is generated (descendants can override the
'voice-volume' value and may therefore generate audio output). Conversely, the latter
requires no time and is not rendered in the aural dimension (descendants can override the
'speak' value and may therefore generate audio output). </p>
</dd>
<dt>
<strong>linear</strong>
</dt>
<dd>
<p> When present, this keyword indicates that the associated value represents a point on a
linear volume amplitude scale, from '0' (silent) to '100' (full volume). Otherwise, the
scale corresponds to monotonically non-decreasing volume levels from '0' (minimum audible)
to '100' (maximum tolerable), with arbitrary intermediary values that depend on the user
environment (see the definition of <non-negative number> below).</p>
</dd>
<dt><strong>x-soft</strong>, <strong>soft</strong>, <strong>medium</strong>,
<strong>loud</strong>, and <strong>x-loud</strong></dt>
<dd>
<p> This sequence of values corresponds to monotonically non-decreasing volume levels. The
value 'x-soft' maps to 0, 'soft' maps to 25, 'medium' maps to 50, 'loud' maps to 75 and
'x-loud' maps to 100. The interpretation of the corresponding numerical values depends on
whether the 'linear' keyword is used (see the definition of <non-negative number>
below).</p>
</dd>
<dt>
<strong><non-negative number></strong>
</dt>
<dd>
<p>An integer or floating point <a href="#non-negative-number-def">positive number</a> in
the range '0' to '100'. The interpretation of the '0' to '100' scale depends on whether
the 'linear' keyword is used.</p>
<p> When the 'linear' keyword not used, '0' represents the <em>minimum audible</em> level,
'100' corresponds to the <em>maximum tolerable</em> level, and '50' corresponds to the
user's <em>preferred</em> volume level. All 3 values are configured by the user, or at
least predefined by the user-agent. The numerical values on this scale are mapped to
concrete volume levels that depend on the user context, so this allows authors to write a
single style sheet that works in a variety of listening environments. </p>
<p> When the 'linear' keyword is specified, '0' maps to 'silent' and '100' maps to the
maximum possible audio volume output (which depends on the user agent implementation,
device capabilities, etc.). The values in between '0' and '100' are placed on a linear
amplitude scale that do not necessarily match the user's expectations, because it is
independent from the user-configured volume levels. For example, '50' may not correspond
to the user's <em>preferred</em> volume level, and it may actually result in louder or
softer audio output than desired. This feature is provided to maintain compatibility with
SSML (where 'x-soft' always means "silent", etc.). </p>
</dd>
<dt>
<strong><percentage></strong>
</dt>
<dd>
<p> Only positive <a href="#percentage-def">percentage</a> values are allowed. Computed
values are calculated relative to the inherited value, and are then clipped to the range
'0' to '100'. The 'linear' keyword is preserved from the inherited value.</p>
<p class="note"> Note that a leading "+" sign does not denote an increment. For example,
+50% is equivalent to 50%, so the computed value equals the inherited value times 0.5
(divided by 2), then clipped to [0,100]. </p>
</dd>
</dl>
<p class="note"> Unless 'linear' is used, the actual volume levels resulting from the use of the
numerical or keyword values depend on various factors, such as the listening environment and
personal user preferences. The effective volume variation between '0' and '100' determines the
dynamic range of the speech output, which is typically compressed in a noisy environment (the
volume corresponding to '0' is nearer the value of '100'), whereas a noise-free context allows
for the full range of volume levels (the gap between '0' and '100' is wider). Conversely,
there may be situations whereby both '0' and '100' are set to low volume levels (for example
when listening discretely at night). </p>
<h3 id="mixing-props-voice-balance">The 'voice-balance' property</h3>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="voice-balance">voice-balance</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td><number> | left | center | right | leftwards | rightwards | inherit</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>center</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>yes</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>N/A</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>The 'voice-balance' property manipulates the distribution of audio output between left and
right channels in stereo-capable sound devices.</p>
<p class="note"> Note that the functionality provided by this property has no match in the SSML
markup language [[!SPEECH-SYNTHESIS]]. </p>
<dl>
<dt>
<strong><number></strong>
</dt>
<dd>
<p>An integer or floating point <a href="#number-def">number</a> between '-100' and '100'.
For '-100' only the left channel is audible. Simarly for '100' only the right channel is
audible. For '0' both channels have the same level, so that the speech appears to be
coming from the center.</p>
</dd>
<dt>
<strong>left</strong>
</dt>
<dd>
<p>Same as '-100'.</p>
</dd>
<dt>
<strong>center</strong>
</dt>
<dd>
<p>Same as '0'.</p>
</dd>
<dt>
<strong>right</strong>
</dt>
<dd>
<p>Same as '100'.</p>
</dd>
<dt>
<strong>leftwards</strong>
</dt>
<dd>
<p>Moves the sound to the left, relative to the inherited 'voice-balance'. More precisely,
subtract 20 from the inherited value and clip the resulting value to the range '-100' and
'100'.</p>
</dd>
<dt>
<strong>rightwards</strong>
</dt>
<dd>
<p>Moves the sound to the right, relative to the inherited 'voice-balance'. More precisely,
add 20 to the inherited value and clip the resulting value to the range '-100' and
'100'.</p>
</dd>
</dl>
<p class="note"> Note that many speech synthesizers only generate mono sound, and therefore do
not intrinsically support the 'voice-balance' property. The distribution of audio signals
between left and right channels would consequently occur at post-synthesis stage, for example
when a speech-enabled user-agent mixes the various audio sources that may be authored within
the document. </p>
<h2 id="speaking-props">Speaking properties</h2>
<h3 id="speaking-props-speak">The 'speak' property</h3>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="speak">speak</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td>auto | none | normal | inherit</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>auto</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>yes</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>N/A</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>The 'speak' property determines whether or not to render text aurally.</p>
<p class="note"> Note that the functionality provided by this property has no match in the SSML
markup language [[!SPEECH-SYNTHESIS]]. </p>
<dl>
<dt>
<strong>auto</strong>
</dt>
<dd>
<p>Resolves to a computed value of 'none' when 'display' is 'none', otherwise resolves to a
computed value of 'auto' which yields a used value of 'normal'. </p>
<p class="note"> Note that 'display' is the only property defined externally to this CSS3
module that affects behavior within the aural "box" model. Also note that the 'none' value
of the 'display' property cannot be overridden by descendants of the selected element, but
the 'auto' value of 'speak' can however be overridden using either of 'none' or 'normal'.
</p>
</dd>
<dt>
<strong>none</strong>
</dt>
<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 'none' 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>
</dd>
<dt>
<strong>normal</strong>
</dt>
<dd>
<p> The element is rendered aurally (regardless of its 'display' value and the 'display' and
'speak' 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>
</dd>
</dl>
<h3 id="speaking-props-speak-as">The 'speak-as' property</h3>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="speak-as">speak-as</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td>normal | spell-out || digits || [ literal-punctuation | no-punctuation ] |
inherit</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>normal</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>yes</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>N/A</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>The 'speak-as' property determines in what manner text gets rendered aurally, based upon a
basic predefined list of possible values.</p>
<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 [[!SPEECH-SYNTHESIS]]. Also note that possible values are
described in a <a href="http://www.w3.org/TR/ssml-sayas">W3C note</a> separate from the SSML
specification, whereas the CSS Speech Module explicitly defines a list of possible values. </p>
<dl>
<dt>
<strong>normal</strong>
</dt>
<dd>
<p>Uses language-dependent pronunciation rules for rendering an element and its children.
Punctuation is not to be spoken, but instead rendered naturally as various pauses.</p>
</dd>
<dt>
<strong>spell-out</strong>
</dt>
<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 "rôle" can
also be written as "role". A conforming implementation would thus be able to spell-out
"rôle" as "R O L E".</p>
</dd>
<dt>
<strong>digits</strong>
</dt>
<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 'speak-as' 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>
</dd>
<dt>
<strong>literal-punctuation</strong>
</dt>
<dd>
<p>Similar to 'normal' value, but punctuation such as semicolons, braces, and so on are to
be spoken literally.</p>
</dd>
<dt>
<strong>no-punctuation</strong>
</dt>
<dd>
<p>Similar to 'normal' value but punctuation is not to be spoken nor rendered as various
pauses.</p>
</dd>
</dl>
<h2 id="pause-props">Pause properties </h2>
<h3 id="pause-props-pause-before-after">The 'pause-before' and 'pause-after' properties</h3>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="pause-before">pause-before</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td><time> | none | x-weak | weak | medium | strong | x-strong | inherit</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>none</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>no</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>N/A</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>specified value</td>
</tr>
</tbody>
</table>
<p> </p>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="pause-after">pause-after</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td><time> | none | x-weak | weak | medium | strong | x-strong | inherit</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>none</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>no</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>N/A</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>specified value</td>
</tr>
</tbody>
</table>
<p>The 'pause-before' and 'pause-after' 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 'cue-before' (or 'cue-after') is specified, before (or after) the
cue within the <a href="#aural-model">audio "box" model</a>.</p>
<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 [[!SPEECH-SYNTHESIS]]. </p>
<dl>
<dt>
<strong><time></strong>
</dt>
<dd>
<p>Expresses the pause in absolute time units (seconds and milliseconds, e.g. "+3s",
"250ms") as per the syntax of <a href="#time-def">time</a> values defined in [[!CSS3VAL]].
Only positive values are allowed.</p>
</dd>
<dt>
<strong>none</strong>
</dt>
<dd>
<p> Equivalent to 0ms (no prosodic break in the speech output). This value can be used to
inhibit a prosodic break which the processor would otherwise produce. </p>
</dd>
<dt>
<strong>x-weak</strong>, <strong>weak</strong>, <strong>medium</strong>,
<strong>strong</strong>, and <strong>x-strong</strong>
</dt>
<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>
</dd>
</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. </p>
<p> The following 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>
<div class="example">
<pre>
p { pause: none } /* pause-before: none; pause-after: none */
</pre>
</div>
<h3 id="pause-props-pause">The 'pause' shorthand property</h3>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="pause">pause</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td><'pause-before'> || <'pause-after'></td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>N/A (see individual properties)</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>no</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>N/A</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>N/A (see individual properties)</td>
</tr>
</tbody>
</table>
<p>The 'pause' property is a shorthand property for 'pause-before' and 'pause-after'. If two
values are given, the first value is 'pause-before' and the second is 'pause-after'. If only
one value is given, it applies to both properties.</p>
<div class="example">
<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">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. </p>
<p class="note"> 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>
<p>The following pauses are adjoining:</p>
<ol>
<li>The 'pause-after' of an aural "box" and the 'pause-after' of its last child, provided the
former has no 'rest-after' and no 'cue-after'.</li>
<li>The 'pause-before' of an aural "box" and the 'pause-before' of its first child, provided
the former has no 'rest-before' and no 'cue-before'.</li>
<li>The 'pause-after' of an aural "box" and the 'pause-before' of its next sibling.</li>
<li>The 'pause-before' and 'pause-after' of an aural "box", if the the "box" has a
'voice-duration' of "0ms" and no 'rest-before' or 'rest-after' and no 'cue-before' or
'cue-after', or if the the "box" has no rendered content at all (see 'speak').</li>
</ol>
<p>A collapsed pause is considered adjoining to another pause if any of its component pauses is
adjoining to that pause.</p>
<p class="note"> Note that 'pause' has been moved from between the element's contents and any
'cue' to outside the 'cue'. This is not backwards compatible with the informative CSS2.1 Aural
appendix [[!CSS21]].</p>
<h2 id="rest-props">Rest properties</h2>
<h3 id="rest-props-rest-before-after">The 'rest-before' and 'rest-after' properties</h3>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="rest-before">rest-before</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td><time> | none | x-weak | weak | medium | strong | x-strong | inherit</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>none</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>no</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>N/A</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>specified value</td>
</tr>
</tbody>
</table>
<p> </p>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td>
<dfn id="rest-after">rest-after</dfn>
</td>
</tr>
<tr>
<td>
<em>Value:</em>
</td>
<td><time> | none | x-weak | weak | medium | strong | x-strong | inherit</td>
</tr>
<tr>
<td>
<em>Initial:</em>
</td>
<td>none</td>
</tr>
<tr>
<td>
<em>Applies to:</em>
</td>
<td>all elements</td>
</tr>
<tr>
<td>
<em>Inherited:</em>
</td>
<td>no</td>
</tr>
<tr>
<td>
<em>Percentages:</em>
</td>
<td>N/A</td>
</tr>
<tr>
<td>