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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>CSS3 Speech Module</title>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii"/>
<link rel="stylesheet" type="text/css" href="http://dev.w3.org/csswg/default.css">
<style type="text/css">
.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; }
</style>
<style type="text/css">
/*<![CDATA[*/
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% }
*:target {
border: 1px dashed #66CC66;
}
/*]]>*/
</style>
<!-- link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-WD.css" -->
<link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED">
</head>
<body>
<div class="head">
<!--logo-->
<h1 id="top">CSS3 Speech Module</h1>
<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
<dl>
<dt>This version:
<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>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-speech">[LATEST]</a>
<dt>Previous versions:
<dd><a href="http://www.w3.org/TR/2004/WD-css3-speech-20041216/">http://www.w3.org/TR/2004/WD-css3-speech-20041216/</a>
<dt id="editors-list">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>
<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 id="abstract" class="no-num no-toc">Abstract</h2>
<p>CSS (Cascading Style Sheets) is a language for describing the
rendering of HTML and XML documents on screen, on paper, in speech,
etc. CSS defines aural properties that give control over rendering
XML and HTML to speech. This draft describes the text to speech properties
proposed for CSS level 3,
and is a re-work of the informative CSS2.1 Aural appendix [[CSS21]].
These are designed for match the model
described in the Speech Synthesis Markup Language (SSML) Version 1.0
[[!SPEECH-SYNTHESIS]].</p>
<p>The CSS3 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>
<h2 id="status" class="no-num no-toc">Status of this document</h2>
<!--status-->
<hr>
<p>This document is a draft of one of the "modules" for the
upcoming CSS3 specification.</p>
<p>This document has been developed in
cooperation with the <a href="/Voice/Group/">Voice Browser working
group</a> (<a href="http://cgi.w3.org/MemberAccess/AccessRequest">W3C
Members only</a>).</p>
<p> </p>
<!-- p>The following features are judged "at risk" and may be dropped at the
end of the CR period,
especially if there has not been enough interest from implementers:
<ul>
</ul>
</p -->
<!-- li><a href="#issue-mark">mark</a></li -->
<p>The following issues need to be discussed and require working group resolutions:
<ul>
<li><a href="#issue-phonemes">'phonemes' property breaks principle of content/presentation separation</a></li>
<li><a href="#issue-speakability-name">'speakability' not an ideal property name ?</a></li>
<li><a href="#issue-lists">handling of list styles, numbered items</a></li>
</ul>
</p>
<!-- li><a href="#issue-voice-cues-volume">audio cues volume level relative to voice-volume</a></li -->
<!-- li><a href="#issue-speak_none">speak:none</a></li -->
<p>The CSS WG maintains an <a href="http://www.w3.org/Style/CSS/Tracker/products/29">issues
list</a> for this module.</p>
<h2 id="contents" class="no-num no-toc">Table of contents</h2>
<!--toc-->
<hr />
<h2 id="dependencies"><span class="secno">1. </span>Dependencies on other
modules</h2>
<p>This CSS3 module depends on the following other CSS3
modules:</p>
<ul>
<li>Values and Units [[!CSS3VAL]]</li>
<li>The box model [[!CSS3BOX]]</li>
</ul>
<p>It has non-normative (informative) references to the following
other CSS3 modules:</p>
<ul>
<li>Cascade and Inheritance [[CSS3CASCADE]]</li>
<li>Generated and Replaced Content [[CSS3GENCON]]</li>
<li>Syntax [[CSS3SYN]]</li>
<!-- li>Tables [[CSS3TBL]]</li -->
<!-- li>Selectors [[SELECT]]</li -->
</ul>
<h2 id="introduction"><span class="secno">2. </span>Introduction</h2>
<p>The speech rendering of a document, already commonly used by
the blind and print-impaired communities, combines speech synthesis
and "auditory icons". Often such aural presentation occurs by
converting the document to plain text and feeding this to a
<dfn>screen reader</dfn> — software or hardware that simply
reads all the characters on the screen. This results in less
effective presentation than would be the case if the document
structure were retained. Style sheet properties for text to speech
may be used together with visual properties (mixed media) or as
an aural alternative to visual presentation.</p>
<p>Besides the obvious accessibility advantages, there are other
large markets for listening to information, including in-car use,
industrial and medical documentation systems (intranets), home
entertainment, and to help users learning to read or who have
difficulty reading.</p>
<p>When using voice properties, the canvas consists of a two
channel stereo space and a temporal space (you can specify
<a href="#cue-props">audio cues</a>
before and after synthetic speech). The CSS properties also
allow authors to vary the characteristics of synthetic speech
(voice type, frequency, inflection, etc.).</p>
<div class="example">
<p>Examples:</p>
<pre>
h1, h2, h3, h4, h5, h6 {
voice-family: paul;
voice-stress: moderate;
cue-before: url(ping.au)
}
p.heidi { voice-balance: left; voice-family: female }
p.peter { voice-balance: right; voice-family: male }
p.goat { voice-volume: soft }
</pre>
<p>This will direct the speech synthesizer to speak headers in a
voice (a kind of "audio font") called "paul". Before speaking the
headers, a sound sample will be played from the given URL.
Paragraphs with class "heidi" will appear to come from the left
(if the sound system is capable of stereo), and paragraphs of class
"peter" from the right. Paragraphs with class "goat" will be played
softly.</p>
</div>
<p class="note">
Note that content creators may conditionally include CSS properties
authored specifically for user-agents with text to speech capabilities (TTS),
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
(the "aural" media type was deprecated in the informative CSS2.1 Aural appendix [[CSS21]]).
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>
<h2 id="aural-model"><span class="secno">3. </span>The aural "box" model</h2>
<p>The formatting model of CSS for aural media is based on a sequence
of sounds and silences that appear in a nested model which is
related to the visual box model; however the aural canvas is one-dimensional,
monolinear. For compatibility with the visual box model, we will call
it the <dfn id="aural-box-model">aural "box" model</dfn>.</p>
<p>The element is surrounded by, in this order, 'rest', 'cue'
and 'pause' properties - they can be thought of as aural equivalents
to 'padding', 'border' and 'margin' respectively.</p>
<p>It can be represented in the following way (including the equivalent
properties from the visual box model for clarification of relationships):</p>
<p><img id="aural-box" src="aural-box.png" alt="A graph depicting the aural 'box' model."/></p>
<p>where <dfn><element></dfn> is the selected element to which the properties
from the CSS3 Speech Module apply.</p>
<p class="note">
Note that the 'none' value of the 'display' property
(which is defined in the CSS box model [[!CSS3BOX]]
and which applies to all media types)
influences the resolved value of the 'speakability' property
(defined within this CSS3 module) when the 'auto' value is specified for 'speakability'.
This is the only case whereby a property defined externally to this CSS3 module
affects a characteristic specific to the aural dimension (i.e. has an impact within the aural "box" model).
</p>
<h2 id="mixing-props"><span class="secno">4. </span>Mixing properties:
'voice-volume' and
'voice-balance'</h2>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="voice-volume">voice-volume</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<td><non-negative number> | <percentage> | silent | x-soft | soft |
medium | loud | x-loud | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>medium</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>yes</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>refer to inherited value</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p>The 'voice-volume' refers to the amplitude of the waveform output by
the speech synthesiser. This may be mixed with other audio sources,
influencing the perceived loudness of synthetic speech relative
to these sources.
</p>
<!-- p>
'voice-volume' does not apply to <a href
="#cue-props">audio cues</a> for which there is a separate means
to set loudness (absolute, or relative to 'voice-volume').
<span class="issue" id="issue-voice-cues-volume">
ISSUE: shouldn't audio cues be subjected to the voice-volume,
so that an inaudible element gets its entire content (within the aural "box" model) muted as well ?
The rationale is that voice-volume:silent is largely equivalent to visibility:hidden,
which affects border, padding and spacing (i.e. the entire content with regards to the CSS "visual" box model).
The audio cues should therefore only be allowed to set their volume levels <em>relatively</em> to the inherited voice-volume, not with absolute values as these may incorrectly enable audio output when the voice-volume itself is muted.
</span>
</p -->
<p>Values have the following meanings:</p>
<!-- dl>
<dt><strong>auto</strong></dt>
<dd>
Resolves to a computed value of 'medium' when 'visibility' is 'visible' (see [[!CSS3BOX]]),
otherwise resolves to a computed value of 'silent'.
</dd -->
<dt><strong><non-negative number></strong></dt>
<dd>An integer or floating point number in the range '0' to '100'.
'0' represents silence (the <em>minimum</em> level), and 100
corresponds to the <em>maximum</em> level. The volume scale is
linear amplitude.
</dd>
<dt><strong><percentage></strong></dt>
<dd>
Only positive values are allowed.
Computed values are calculated relative to the inherited
value, and are then clipped to the range '0' to '100'.
<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>
<dt><strong>silent</strong>,
<strong>x-soft</strong>,
<strong>soft</strong>,
<strong>medium</strong>,
<strong>loud</strong>, and
<strong>x-loud</strong></dt>
<dd>A sequence of monotonically non-decreasing volume levels. The value
of 'silent' is mapped to '0' and 'x-loud' is mapped to '100'.
The mapping of other values to numerical volume levels is implementation
dependent and may vary from one speech synthesizer to the next.</dd>
</dl>
<p>User agents should allow the level corresponding to '100' to be
set by the listener. No one setting is universally applicable;
suitable values depend on the equipment in use (speakers,
headphones), and the environment (in car, home theater, library)
and personal preferences.</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 'speakability' 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
(although descendants may override the 'voice-volume' value and may therefore generate audio output).
The latter requires no time and is not rendered in the aural dimension
<!-- (including its descendants, which cannot override the inherited 'none' value). -->
(although descendants may override the 'speakability' value and may therefore generate audio output).
</p>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="voice-balance">voice-balance</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<td><number> | left | center | right | leftwards | rightwards | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>center</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>yes</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p>The 'voice-balance' property refers to the balance between
left and right channels, and presumes a two channel (stereo) model
that is widely supported on consumer audio equipment.</p>
<p>Values have the following meanings:</p>
<dl>
<dt><strong><number></strong></dt>
<dd>An integer or floating point number between '-100' and '100'.
For '-100' only the left channel is audible. Simarly for '100' or
'+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.</dd>
<dt><strong>left</strong></dt>
<dd>Same as '-100'.</dd>
<dt><strong>center</strong></dt>
<dd>Same as '0'.</dd>
<dt><strong>right</strong></dt>
<dd>Same as '100' or '+100'.</dd>
<dt><strong>leftwards</strong></dt>
<dd>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'.</dd>
<dt><strong>rightwards</strong></dt>
<dd>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'.</dd>
</dl>
<p>Many speech synthesizers only support a single channel. The
'voice-balance' property can then be treated as part of a post
synthesis mixing step. This is where speech is mixed with other
audio sources.
</p>
<!-- p>Unlike 'voice-volume', 'voice-balance'
<em>does</em> apply to <a href="#cue-props">audio cues</a>.</p -->
<h2 id="speaking-props"><span class="secno">5. </span>Speaking properties:
'speakability', 'speak'</h2>
<!-- <p>An additional speech property, speak-header, is described in the
CSS module covering tables.</p> -->
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="speakability">speakability</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<td>auto | none | normal | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>auto</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>yes</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p class="issue" id="issue-speakability-name">
ISSUE: should the "speakability" property be named differently ? e.g. "speaking"
</p>
<p>This property specifies whether text will be rendered aurally.</p>
<p>Values have the following meanings:</p>
<dl>
<dt><strong>auto</strong></dt>
<dd>
Resolves to a computed value of 'none' when 'display' is 'none' (see [[!CSS3BOX]]),
otherwise resolves to a computed value of 'auto' which yields a used value of 'normal'.
</dd>
<dt><strong>none</strong></dt>
<dd>
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 class="note">
Note that any of the descendants of the affected element
are allowed to override this value, so they may actually take part in the aural rendering.
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 adjacent rests.
</p>
<!--
Descendant elements do not get rendered either;
this behavior cannot be overridden by setting the 'speakability' property on the descendants.
-->
</dd>
<dt><strong>normal</strong></dt>
<dd>
The element is rendered aurally.
</dd>
</dl>
<p class="note">
Note that although the 'none' value of the 'display' property cannot be overridden by descendants of the affected element (see [[!CSS3BOX]]),
the 'auto' value of 'speakability' can however be overridden by descendants, using either of 'none' or 'normal'.
In the case of 'normal', this would result in descendants being rendered in the aural dimension even though they would not be rendered on the visual canvas.
<!-- To ensure that an element <em>and its descendants</em> do not get rendered in the aural dimension,
use the 'none' value for the 'speakability' property. -->
</p>
<!-- p class="note">
Note that the value of the 'visibility' property (see [[!CSS3BOX]])
may affect the computed value of 'voice-volume', but do not affect the 'speakability' property.
</p -->
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="speak">speak</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<td>normal | spell-out | digits | literal-punctuation |
no-punctuation | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>normal</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>yes</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p>This property specifies in what manner text gets rendered aurally.</p>
<p>Values have the following meanings:</p>
<dl>
<dt><strong>normal</strong></dt>
<dd>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.</dd>
<dt><strong>spell-out</strong></dt>
<dd>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".</dd>
<dt><strong>digits</strong></dt>
<dd>Speak numbers one digit at a time, for instance, "twelve" would
be spoken as "one two", and "31" as "three one".</dd>
<dt><strong>literal-punctuation</strong></dt>
<dd>Similar to 'normal' value, but punctuation such as semicolons,
braces, and so on are to be spoken literally.</dd>
<dt><strong>no-punctuation</strong></dt>
<dd>Similar to 'normal' value but punctuation is not to be spoken
nor rendered as various pauses.</dd>
</dl>
<p>Speech synthesizers are knowledgeable about what is and what is
not a number. The 'speak' property gives authors the means to control
how the synthesizer renders the numbers it discovers in the source
text, and may be implemented as a preprocessing step before passing
the text to the speech synthesizer.</p>
<h2 id="pause-props"><span class="secno">6. </span>Pause properties:
'pause-before',
'pause-after' and
'pause'
<!-- a href="#collapsing">collapsing pauses</a -->
</h2>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="pause-before">pause-before</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<td><time> | none | x-weak | weak | medium | strong
| x-strong | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>implementation dependent</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</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 width="20%"><em>Value:</em></td>
<td><time> | none | x-weak | weak | medium | strong
| x-strong | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>implementation dependent</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p>These properties specify a pause or prosodic boundary to be
observed before (or after) an element or, if any 'cue-before' (or
'cue-after') is specified, before (or after) these.</p>
<p>Values have the following meanings:</p>
<dl>
<dt><strong><time></strong></dt>
<dd>Expresses the pause in absolute time units, as per the syntax of "time" values in [[!CSS3VAL]] (seconds and
milliseconds, e.g. "3s", "250ms"). Only positive values are allowed.</dd>
<dt><strong>none</strong>,
<strong>x-weak</strong>,
<strong>weak</strong>,
<strong>medium</strong>,
<strong>strong</strong>, and
<strong>x-strong</strong>
</dt>
<dd>These values may be used to indicate the prosodic strength of
the break in speech output. The synthesis processor may insert a
pause as part of its implementation of the prosodic break. The value
"none" indicates that no prosodic break boundary should be output,
and can be used to inhibit a prosodic break which the processor
would otherwise produce. The other values indicate monotonically
non-decreasing (conceptually increasing) break strength between
elements. "x-weak" and "x-strong" are mnemonics for "extra weak" and "extra
strong", respectively. The stronger boundaries are typically accompanied by pauses.
The breaks between paragraphs are typically much stronger than the breaks between words within a sentence.</dd>
</dl>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="pause">pause</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<td>[ <'pause-before'> || <'pause-after'> ] |
inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>implementation dependent</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p>The 'pause' property is a shorthand for setting '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:</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. Adjacent pauses should be merged
by selecting the strongest named break or the longest absolute
time interval. Thus "strong" is selected when comparing "strong"
and "weak", while "1s" is selected when comparing "1s" and "250ms".
We say that such pauses <dfn id="collapse">collapse</dfn>.
A combination of a named break and time duration is treated
additively.</p>
<p>The following pauses collapse:</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", no 'rest-before' or 'rest-after', no
'cue-before' or 'cue-after' and no content.</li>
</ol>
<p>The 'pause-after' of an element is always adjoining to the 'pause-before' of its
next sibling.</p>
<p>The 'pause-before' an element is adjoining to its first child's 'pause-before',
if the element has no 'cue-before' nor 'rest-before'.</p>
<p>The 'pause-after' of an element is adjoining to its last child's 'pause-after',
if the element has no 'rest-after' or 'cue-after'.</p>
<p>An element's own pauses are adjoining if the 'voice-duration' property
is zero, and it has no rest, and it does not contain any content,
and all of its children's pauses (if any) are adjoining.</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"><span class="secno">7. </span>Rest properties:
'rest-before',
'rest-after' and
'rest'</h2>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="rest-before">rest-before</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<td><time> | none | x-weak | weak | medium | strong
| x-strong | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>implementation dependent</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</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 width="20%"><em>Value:</em></td>
<td><time> | none | x-weak | weak | medium | strong
| x-strong | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>implementation dependent</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p>These properties specify a rest or prosodic boundary to be observed
before (or after) speaking an element's content.</p>
<p>Values have the following
meanings:</p>
<dl>
<dt><strong><time></strong></dt>
<dd>Expresses the rest in absolute time units, as per the syntax of "time" values in [[!CSS3VAL]] (seconds and milliseconds,
e.g. "3s", "250ms"). Only positive values are allowed.</dd>
<dt><strong>none</strong>,
<strong>x-weak</strong>,
<strong>weak</strong>,
<strong>medium</strong>,
<strong>strong</strong>, and
<strong>x-strong</strong>
</dt>
<dd>These values may be used to indicate the prosodic strength of
the break in speech output. The synthesis processor may insert a
rest as part of its implementation of the prosodic break. The value
"none" indicates that no prosodic break boundary should be output,
and can be used to inhibit a prosodic break which the processor
would otherwise produce. The other values indicate monotonically
non-decreasing (conceptually increasing) break strength between words.
The stronger boundaries are typically accompanied by rests. "x-weak"
and "x-strong" are mnemonics for "extra weak" and "extra strong",
respectively.</dd>
</dl>
<p>As opposed to <a href="#pause-props">pause properties</a>, the
rest is inserted between the element's content and any 'cue-before'
or 'cue-after' content. Adjacent rests are treated additively.</p>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="rest">rest</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<td>[ <'rest-before'> || <'rest-after'> ] | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>implementation dependent</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>N/A</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p>The 'rest' property is a shorthand for setting 'rest-before' and
'rest-after'. If two values are given, the first value is 'rest-before'
and the second is 'rest-after'. If only one value is given, it applies
to both properties.</p>
<h2 id="cue-props"><span class="secno">8. </span>Cue properties:
'cue-before',
'cue-after' and
'cue'</h2>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>
<td>Name:</td>
<td><dfn id="cue-before">cue-before</dfn></td>
</tr>
<tr>
<td width="20%"><em>Value:</em></td>
<!-- td><uri> [<non-negative number> | <percentage> | silent
| x-soft | soft | medium | loud | x-loud] | none | inherit</td -->
<td><uri> [<percentage>] | none | inherit</td>
</tr>
<tr>
<td width="20%"><em>Initial:</em></td>
<td>none</td>
</tr>
<tr>
<td width="20%"><em>Applies to:</em></td>
<td>all elements</td>
</tr>
<tr>
<td width="20%"><em>Inherited:</em></td>
<td>no</td>
</tr>
<tr>
<td width="20%"><em>Percentages:</em></td>
<td>apply to inherited value for 'voice-volume'</td>
</tr>
<tr>
<td width="20%"><em>Media:</em></td>
<td>speech</td>
</tr>
</tbody>
</table>
<p> </p>
<table class="propdef" summary="name: syntax">
<tbody>
<tr>