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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" />
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED" rel="stylesheet" type="text/css" />
<!-- link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-WD.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%
}
-->
</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 [[!SSML]]. 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-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 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, 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>
<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. </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>
<h2 id="values">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 [[!CSS21]]. Value types not defined in this
specification are defined in CSS Value and Units Level 3 [[!CSS3VAL]]. </p>
<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. </p>
<h2 id="example">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 (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>
<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;
}
...
<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 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 '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. When used, the ':before' and
':after' pseudo-elements [[!CSS21]] get inserted between the element's contents and the
'rest'. </p>
<p> 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] || <decibel>] </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>N/A</td>
</tr>
<tr>
<td>
<em>Media:</em>
</td>
<td>speech</td>
</tr>
<tr>
<td>
<em>Computed value:</em>
</td>
<td>a keyword value, and optionally also a decibel offset (if not zero)</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 when calculating 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 [[!SSML]]. </p>
<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>
</dt>
<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 'voice-volume'
property has a value of 'silent', and an element whose 'speak' property has the value
'none'. 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 'voice-volume' 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 'speak' value and may therefore
generate audio output). </p>
</dd>
<dt><strong>x-soft</strong>, <strong>soft</strong>, <strong>medium</strong>,
<strong>loud</strong>, <strong>x-loud</strong></dt>
<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 'x-soft' maps to
the user's <em>minimum audible</em> volume level, 'x-loud' maps to the user's <em>maximum
tolerable</em> volume level, 'medium' maps to the user's <em>preferred</em> volume
level, 'soft' and 'loud' map to intermediary values. </p>
</dd>
<dt>
<strong><decibel></strong>
</dt>
<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 'silent', this 'voice-volume' resolves to 'silent' too,
regardless of the specified <decibel> 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>
</dd>
</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 'x-soft' and 'x-loud' 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 'x-soft' would effectively be closer to 'x-loud' than it
would be in a quiet environment. There may also be situations where both 'x-soft' and 'x-loud'
would map to low volume levels, such as in listening environments requiring discretion (e.g.
library, night-reading). </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 </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>the specified value resolved to a <number> between '-100' and '100'
(inclusive)</td>
</tr>
</tbody>
</table>
<p> The 'voice-balance' 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>
<p class="note"> Note that the functionality provided by this property has no match in the SSML
markup language [[!SSML]]. </p>
<dl>
<dt>
<strong><number></strong>
</dt>
<dd>
<p>A <a href="#number-def">number</a> between '-100' and '100' (inclusive). Values smaller
than '-100' are clamped to '-100'. Values greater than '100' are clamped to '100'. The
value '-100' represents the left side, and the value '100' represents the right side. The
value '0' 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>
</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, by subtracting 20 from the inherited 'voice-balance' value,
and by clamping the resulting number to '-100'.</p>
</dd>
<dt>
<strong>rightwards</strong>
</dt>
<dd>
<p>Moves the sound to the right, by adding 20 to the inherited 'voice-balance' value, and by
clamping the resulting number to '100'.</p>
</dd>
</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: </p>
<ul>
<li> When user-agents produce audio via a mono-aural sound system (i.e. single-speaker setup),
the 'voice-balance' property has no effect. </li>
<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 'voice-balance' property. </li>
<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 'voice-balance' 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 'center' value. </li>
</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
'voice-balance' 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: </p>
<ul>
<li>The value '0' maps to zero degrees ('center'). This is in "front" of the listener, not
from "behind".</li>
<li>The value '-100' maps to -40 degrees ('left'). Negative angles are in the
counter-clockwise direction (the audio stage is seen from the top).</li>
<li>The value '100' maps to 40 degrees ('right'). Positive angles are in the clockwise
direction (the audio stage is seen from the top).</li>
<li>Intermediary values on the scale from '-100' to '100' map to the angles between -40 and 40
degrees in a numerically linearly-proportional manner. For example, '-50' maps to -20
degrees.</li>
</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 'voice-balance' property would obviously not be perceivable at
all. The rendering fidelity of authored content is therefore dependent on such user
customizations, and the 'voice-balance' property merely specifies the desired end-result. </p>
<p class="note"> Note that many speech synthesizers only generate mono sound, and therefore do
not intrinsically support the 'voice-balance' 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) </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 </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 [[!SSML]]. </p>
<dl>
<dt>
<strong>auto</strong>
</dt>
<dd>
<p>Resolves to a computed value of 'none' when <a href="#display-def">'display'</a> is
'none', otherwise resolves to a computed value of 'auto' which yields a used value of
'normal'. </p>
<p class="note"> Note that the 'none' value of the <a href="#display-def">'display'</a>
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 <a href="#display-def">'display'</a>
value and the <a href="#display-def">'display'</a> 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 ] </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 [[!SSML]], whose values are described in the [[SSML-SAYAS]] W3C
Note. </p>
<dl>
<dt>
<strong>normal</strong>
</dt>
<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>
</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> Punctuation such as semicolons, braces, and so on is named aloud (i.e. spoken literally)
rather than rendered naturally as appropriate pauses.</p>
</dd>
<dt>
<strong>no-punctuation</strong>
</dt>
<dd>
<p>Punctuation is not rendered: neither spoken nor rendered as 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 </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 </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 [[!SSML]]. </p>
<dl>
<dt>
<strong><time></strong>
</dt>
<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>
</dd>
<dt>
<strong>none</strong>
</dt>
<dd>
<p> Equivalent to 0ms (no prosodic break is produced by the speech processor). </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>
<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">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">
<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">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>
<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 </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>