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<h1>CSS Text Module Level 3</h1>
<pre class='metadata'>
Shortname: css-text
Level: 3
Status: ED
Deadline: 2014-09-20
Group: csswg
ED: http://dev.w3.org/csswg/css-text-3/
TR: http://www.w3.org/TR/css-text-3/
Previous Version: http://www.w3.org/TR/2012/WD-css3-text-20121113/
!Issue Tracking: <a href="http://www.w3.org/Style/CSS/Tracker/products/10">http://www.w3.org/Style/CSS/Tracker/products/10</a>
Test Suite: http://test.csswg.org/suites/css3-text/nightly-unstable/
Editor: fantasai, Invited Expert, http://fantasai.inkedblade.net/contact
Editor: Koji Ishii, Invited Expert, kojiishi@gluesoft.co.jp
Abstract: This CSS3 module defines properties for text manipulation and specifies their processing model. It covers line breaking, justification and alignment, white space handling, and text transformation.
At Risk: the ''full-width'' value of 'text-transform'
At Risk: the <length> values of the 'tab-size' property
At Risk: the 'text-justify' property
At Risk: the percentage values of 'word-spacing'
At Risk: the 'hanging-punctuation' property
</pre>
<style type="text/css">
img { vertical-align: middle; }
span[lang] { font-size: 125%; line-height: 1; vertical-align: middle;}
/* Bidi & spaces example */
.egbidiwsaA,.egbidiwsbB,.egbidiwsaB,.egbidiwsbC
{ white-space:pre;font-size:80%;font-family:monospace; vertical-align:2px; margin:1px }
.egbidiwsaA { background:lime;padding:2px; }
.egbidiwsbB { border:2px solid blue }
.egbidiwsaB { background:yellow;border:2px dotted white }
.egbidiwsbC { border:2px dotted red }
.hyphens-ex {
border: thin solid black;
display: inline-block;
padding: 4pt;
}
/* Start Letter-spacing Tutorial */
.ls-ex {
font-size: 200%;
margin-left: 1em;
margin-right: 1em;
}
.ls-fixed-width {
width: 10em;
}
.color-box { background: rgb(224, 203, 82); }
.bad { color: red; }
.good { color: green; }
/* End Letter-spacing Tutorial */
.char { border: 1px dotted gray; }
.quarter { font-size: 25%; }
tt[lang="ja"] { font-family: "MS Gothic", "Osaka", monospace }
div.figure table {
margin :auto;
}
.feedback {
background: #FFEECC;
border-color: orange;
}
.feedback:before {
content: "Info Needed";
color: #FF8800;
}
</style>
<h2 id="intro">
Introduction</h2>
<p>This module describes the typesetting controls of CSS;
that is, the features of CSS that control the translation of
source text to formatted, line-wrapped text.
Various CSS properties provide control over
<a href="#transforming">case transformation</a>,
<a href="#white-space">white space collapsing</a>,
<a href="#white-space">text wrapping</a>,
<a href="#line-breaking">line breaking rules</a>
and <a href="#hyphenation">hyphenation</a>,
<a href="#justification">alignment and justification</a>,
<a href="#spacing">spacing</a>,
and <a href="#edge-effects">indentation</a>.
<div class="note">
<p>Font selection is covered in <a href="http://www.w3.org/TR/css3-fonts/">CSS Fonts Level 3</a> [[CSS3-FONTS]].
<p>
<span name="decoration"></span>
<span name="text-decoration"></span>
<span name="line-decoration"></span>
<span name="text-decoration-line"></span>
<span name="text-decoration-color"></span>
<span name="text-decoration-style"></span>
<span name="text-decoration-skip"></span>
<span name="text-underline-position"></span>
<span name="emphasis-marks"></span>
<span name="text-emphasis-style"></span>
<span name="text-emphasis-color"></span>
<span name="text-emphasis"></span>
<span name="text-emphasis-position"></span>
<span name="text-shadow"></span>
Features for decorating text,
such as <a href="http://www.w3.org/TR/css-text-decor-3/#line-decoration">underlines</a>,
<a href="http://www.w3.org/TR/css-text-decor-3/#emphasis-marks">emphasis marks</a>,
and <a href="http://www.w3.org/TR/css-text-decor-3/#text-shadow-property">shadows</a>,
(previously part of this module)
are covered in
<a href="http://www.w3.org/TR/css-text-decor-3/">CSS Text Decoration Level 3</a> [[CSS3-TEXT-DECOR]].
<p><a href="http://www.w3.org/TR/css3-writing-modes/#text-direction">Bidirectional</a> and
<a href="http://www.w3.org/TR/css3-writing-modes/#vertical-intro">vertical</a> text
are addressed in
<a href="http://www.w3.org/TR/css3-writing-modes/">CSS Writing Modes Level 3</a> [[CSS3-WRITING-MODES]].
</div>
<h3 id="placement">
Module Interactions</h3>
<p>This module, together with [[CSS3-TEXT-DECOR]],
replaces and extends the text-level features defined in [[!CSS21]] chapter 16.
<h3 id="values">
Values</h3>
<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 Level 2 Revision 1 [[!CSS21]].
Other CSS modules may expand the definitions of these value types: for
example [[CSS3VAL]], when combined with this module, expands the
definition of the <var><length></var> value type as used in this specification.</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.
<h3 id="terms">
Terminology</h3>
<p>In addition to the terms defined below,
other terminology and concepts used in this specification are defined
in [[!CSS21]] and [[!CSS3-WRITING-MODES]].
<h4 id="characters">
Characters and Letters</h4>
<p>The basic unit of typesetting is the <dfn>character</dfn>.
However, because writing systems are not always as simple as the basic English alphabet,
what a <i>character</i> actually is depends on the context in which the term is used.
For example, in Hangul (the Korean writing system),
each square representation of a syllable
(e.g. <span lang=ko-hang title="Hangul syllable HAN">한</span>=<span lang=ko-Latn>Han</span>)
can be considered a <i>character</i>.
However, the square symbol is really composed of multiple letters each representing a phoneme
(e.g. <span lang=ko-hang title="Hangul letter HIEUH">ㅎ</span>=<span lang=ko-Latn>h</span>,
<span lang=ko-hang title="Hangul letter HIEUH">ㅏ</span>=<span lang=ko-Latn>a</span>,
<span lang=ko-hang title="Hangul letter HIEUH">ㄴ</span>=<span lang=ko-Latn>n</span>)
and these also could each be considered a <i>character</i>.
<p>A basic unit of computer text encoding, for any given encoding,
is also called a <i>character</i>,
and depending on the encoding,
a single encoding <i>character</i> might correspond
to the entire pre-composed syllabic <i>character</i> (e.g. <span lang=ko-hang title="Hangul syllable HAN">한</span>),
to the individual phonemic <i>character</i> (e.g. <span lang=ko-hang title="Hangul letter HIEUH">ㅎ</span>),
or to smaller units such as
a base letterform (e.g. <span lang=ko-hang title="Hangul letter IEUNG">ㅇ</span>)
and any combining marks that vary it (e.g. extra strokes that represent aspiration).
<p>In turn, a single encoding <i>character</i> can be represented in the data stream as one or more bytes;
and in programming environments one byte is sometimes also called a <i>character</i>.
<p>For text layout, we will refer to the <dfn title="typographic character unit|typographic character">typographic character unit</dfn>
as the basic unit of text.
Even within the realm of text layout,
the relevant <i>character</i> unit depends on the operation.
For example, line-breaking and letter-spacing will segment
a sequence of Thai characters that include U+0E33 THAI CHARACTER SARA AM differently;
or the behaviour of a conjunct consonant in a script such as Devanagari
may depend on the font in use.
So the <i>typographic character</i> represents a unit of the writing system—<!--
-->such as a Latin alphabetic letter (including its diacritics),
Hangul syllable,
Chinese ideographic character,
Myanmar syllable cluster—<!--
-->that is indivisible with respect to a particular typographic operation
(line-breaking, first-letter effects, tracking, justification, vertical arrangement, etc.).
<a href="http://www.unicode.org/reports/tr29/">Unicode Standard Annex #29: Text Segmentation</a>
defines a unit called the <dfn>grapheme cluster</dfn>
which approximates the <i>typographic character</i>.
A UA must use the <em>extended grapheme cluster</em>
(not <em>legacy grapheme cluster</em>), as defined in [[!UAX29]],
as the basis for its <i>typographic character unit</i>.
However, the UA should tailor the definitions
as required by typographic tradition
since the default rules are not always appropriate or ideal,
and is expected to tailor them differently
depending on the operation as needed.
<!--
<p class="note">
The rules for such tailorings are out of scope for CSS,
however W3C currently maintains a wiki page
where some known tailorings are collected.
-->
<div class="example">
<p>For example,
in some scripts such as Myanmar or Devanagari,
the <i>typographic character unit</i> for both justification and line-breaking
is an entire syllable,
which can include more than one [[!UAX29]] <i>grapheme cluster</i>.
<p>In other scripts such as Thai or Lao,
even though for line-breaking the <i>typographic character</i>
matches Unicode’s default <i>grapheme clusters</i>,
for letter-spacing the relevant unit
is <em>less</em> than a [[!UAX29]] <i>grapheme cluster</i>,
and may require decomposition or other substitutions
before spacing can be inserted.
<p>For instance,
to properly letter-space the Thai word คำ (U+0E04 + U+0E33),
the U+0E33 needs to be decomposed into U+0E4D + U+0E32,
and then the extra letter-space inserted before the U+0E32: คํ า.
<p>A slightly more complex example is น้ำ (U+0E19 + U+0E49 + U+0E33).
In this case, normal Thai shaping will first decompose the U+0E33 into U+0E4D + U+0E32
and then swap the U+0E4D with the U+0E49, giving U+0E19 + U+0E4D + U+0E49 + U+0E32.
As before the extra letter-space is then inserted before the U+0E32: นํ้ า.
</div>
<p>A <dfn>typographic letter unit</dfn> or <dfn>letter</dfn> for the purpose of this specification
is a <i>typographic character unit</i> belonging to one of the Letter or Number general
categories in Unicode. [[!UAX44]]
See <a href="#character-properties">Character Properties</a>
for how to determine the Unicode properties of a <i>typographic character unit</i>.
<p>The rendering characteristics of a <i>typographic character unit</i> divided
by an element boundary is undefined:
it may be rendered as belonging to either side of the boundary,
or as some approximation of belonging to both.
Authors are forewarned that dividing <i>grapheme clusters</i>
by element boundaries may give inconsistent or undesired results.
<p><dfn>semantically-perceived character</dfn>
<dfn>visually-perceived character</dfn>
<dfn>semantically-perceived letter</dfn>
<dfn>visually-perceived letter</dfn>
<h4 id="languages">
Languages and Typesetting</h4>
<p>The <dfn>content language</dfn> of an element is the (human) language
the element is declared to be in, according to the rules of the
<a href="http://www.w3.org/TR/CSS21/conform.html#doclanguage">document language</a>.
For example, the rules for determining the <i>content language</i> of an HTML
element use the <code>lang</code> attribute and are defined in [[HTML5]],
and the rules for determining the <i>content language</i> of an XML element use
the <code>xml:lang</code> attribute and are
<a href="http://www.w3.org/TR/REC-xml/#sec-lang-tag">defined</a> in [[XML10]].
Note that it is possible for the <i>content language</i> of an element
to be unknown.
<p class="note">
Many typographic effects vary by linguistic context.
In CSS, language-specific typographic tailorings
are only applied when the content language is known (declared).
<strong>Authors should tag their content accurately for the best typographic behavior.</strong>
<h2 id="transforming">
Transforming Text</h2>
<h3 id="text-transform-property">
<span name="caps-prop"></span>
Case Transforms: the 'text-transform' property</h3>
<table class="propdef">
<tr>
<th>Name:</th>
<td><dfn>text-transform</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td>none | capitalize | uppercase | lowercase | full-width
</td>
</tr>
<tr>
<th>Initial:</th>
<td>none</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>as specified</td>
</tr>
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td>N/A
</table>
<p>This property transforms text for styling purposes.
(It has no effect on the underlying content.)
Values have the following meanings:</p>
<dl dfn-for=text-transform dfn-type=value>
<dt><dfn>none</dfn></dt>
<dd>No effects.</dd>
<dt><dfn>capitalize</dfn></dt>
<dd>Puts the first <i>semantically-perceived letter</i> of each word in titlecase; other characters
are unaffected.</dd>
<dt><dfn>uppercase</dfn></dt>
<dd>Puts all <i>semantically-perceived letters</i> in uppercase.
<dt><dfn>lowercase</dfn></dt>
<dd>Puts all <i>semantically-perceived letters</i> in lowercase.</dd>
<dt><dfn>full-width</dfn></dt>
<dd>Puts all characters in fullwidth form.
If the character does not have a corresponding fullwidth form,
it is left as is.
This value is typically used to typeset Latin characters and digits
like ideographic characters.
</dl>
<p>The definition of “word“ used for ''capitalize'' is UA-dependent;
[[!UAX29]] is suggested (but not required) for determining such word
boundaries. Authors should not expect ''capitalize'' to follow
language-specific titlecasing conventions (such as skipping articles
in English).
<div class="example">
<p>The following example converts the ASCII characters
used in abbreviations in Japanese text to their fullwidth variants
so that they lay out and line break like ideographs:
<pre>abbr:lang(ja) { text-transform: full-width; }</pre>
</div>
<p class="note">
As defined in <a href="#order">Text Processing Order of Operations</a>,
this property affects line breaks and other CSS properties.
<p>
The UA must use the full case mappings for Unicode
characters, including any conditional casing rules, as defined in
Default Case Algorithm section of The Unicode Standard [[!UNICODE]].
If (and only if) the <i>content language</i>
of the element is, according to the rules of the
<a href="http://www.w3.org/TR/CSS21/conform.html#doclanguage">document language</a>,
known,
then any appropriate language-specific rules must be applied as well.
These minimally include, but are not limited to, the language-specific
rules in Unicode's
<a href="http://www.unicode.org/Public/UNIDATA/SpecialCasing.txt">SpecialCasing.txt</a>.
<div class="example">
<p>For example, in Turkish there are two “i”s, one with
a dot—“İ” and “i”— and one
without—“I” and “ı”. Thus the usual
case mappings between “I” and “i” are
replaced with a different set of mappings to their respective
undotted/dotted counterparts, which do not exist in English. This
mapping must only take effect if the <i>content language</i> is Turkish
(or another Turkic language that uses Turkish casing rules);
in other languages, the usual mapping of “I”
and “i” is required. This rule is thus conditionally
defined in Unicode's SpecialCasing.txt file.
</div>
<p>The definition of fullwidth and halfwidth forms can be found on the
Unicode consortium web site at [[!UAX11]].
The mapping to fullwidth form is defined by taking code points with
the <code><wide></code> or the <code><narrow></code> tag
in their <code>Decomposition_Mapping</code> in [[!UAX44]].
For the <code><narrow></code> tag,
the mapping is from the code point to the decomposition (minus <code><narrow></code> tag),
and for the <code><wide></code> tag,
the mapping is from the decomposition (minus the <code><wide></code> tag)
back to the original code point.
<p>Text transformation happens after <a href="#white-space-rules">white
space processing</a>, which means that ''full-width'' only transforms
preserved U+0020 spaces to U+3000.
<p class="note">
A future level of CSS may introduce the ability to create custom mapping
tables for less common text transforms, such as by an ''@text-transform''
rule similar to ''@counter-style'' from [[CSS-COUNTER-STYLES-3]].
<h2 id="white-space-property"><span id="white-space-collapsing"></span><span id='text-wrap'></span>
White Space and Wrapping: the 'white-space' property</h2>
<table class="propdef">
<tr>
<th>Name:</th>
<td><dfn>white-space</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td>normal | pre | nowrap | pre-wrap | pre-line</td>
</tr>
<tr>
<th>Initial:</th>
<td>normal
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>as specified
</tr>
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td>N/A
</table>
<p>This property specifies two things:
<ul>
<li>whether and how <i>white space</i> inside the element is collapsed
<li>whether lines may <i>wrap</i> at unforced <i>soft wrap opportunities</i>
</ul>
<p>Values have the following meanings, which must be interpreted
according to
the <a href="#white-space-rules">White Space Processing</a> and
<a href="#line-breaking">Line Breaking</a> rules:</p>
<dl dfn-for=white-space dfn-type=value>
<dt><dfn>normal</dfn></dt>
<dd>This value directs user agents to collapse sequences of <i>white space</i>
into a single character (or <a href="#line-break-transform">in some
cases</a>, no character).
Lines may wrap at allowed <i>soft wrap opportunities</i>,
as determined by the line-breaking rules in effect,
in order to minimize inline-axis overflow.
<dt><dfn>pre</dfn></dt>
<dd>This value prevents user agents from collapsing sequences of <i>white space</i>.
<i>Segment breaks</i> such as line feeds and carriage returns are preserved as <i>forced line breaks</i>.
Lines only break at <i>forced line breaks</i>;
content that does not fit within the block container overflows it.
<dt><dfn>nowrap</dfn>
<dd>Like ''white-space/normal'', this value collapses <i>white space</i>;
but like ''pre'', it does not allow wrapping.
<dt><dfn>pre-wrap</dfn></dt>
<dd>Like ''pre'', this value preserves <i>white space</i>;
but like ''white-space/normal'', it allows wrapping.
<dt><dfn>pre-line</dfn></dt>
<dd>Like ''white-space/normal'', this value collapses consecutive spaces and allows wrapping,
but preserves <i>segment breaks</i> in the source as <i>forced line breaks</i>.
</dl>
<p>The following informative table summarizes the behavior of various
'white-space' values:</p>
<table class="data">
<colgroup class="header"></colgroup>
<colgroup span=3></colgroup>
<thead>
<tr>
<th></th>
<th>New Lines</th>
<th>Spaces and Tabs</th>
<th>Text Wrapping</th>
</tr>
</thead>
<tbody>
<tr>
<th>''white-space/normal''</th>
<td>Collapse</td>
<td>Collapse</td>
<td>Wrap</td>
</tr>
<tr>
<th>''pre''</th>
<td>Preserve</td>
<td>Preserve</td>
<td>No wrap</td>
</tr>
<tr>
<th>''nowrap''</th>
<td>Collapse</td>
<td>Collapse</td>
<td>No wrap</td>
</tr>
<tr>
<th>''pre-wrap''</th>
<td>Preserve</td>
<td>Preserve</td>
<td>Wrap</td>
</tr>
<tr>
<th>''pre-line''</th>
<td>Preserve</td>
<td>Collapse</td>
<td>Wrap</td>
</tbody>
</table>
<p>See <a href="#white-space-processing">White Space Processing Rules</a>
for details on how white space collapses. An informative summary of
collapsing (''white-space/normal'' and ''nowrap'') is presented below:
<ul>
<li>A sequence of segment breaks and other <i>white space</i> between two
Chinese, Japanese, or Yi characters collapses into nothing.
<li>A zero width space before or after a white space sequence
containing a segment break causes the entire sequence of <i>white space</i>
to collapse into a zero width space.
<li>Otherwise, consecutive <i>white space</i> collapses into a single space.
</ul>
<p>See <a href="#line-breaking">Line Breaking</a>
for details on wrapping behavior.
<h2 id="white-space-processing">
White Space Processing Details</h2>
<p>The source text of a document often contains formatting
that is not relevant to the final rendering: for example,
<a href="http://rhodesmill.org/brandon/2012/one-sentence-per-line/"
>breaking the source into segments</a> (lines) for ease of editing
or adding white space characters such as tabs and spaces to indent the source code.
CSS white space processing allows the author to control interpretation of such formatting:
to preserve or collapse it away when rendering the document.
White space processing in CSS interprets white space characters only for rendering:
it has no effect on the underlying document data.
<p>White space processing in CSS is controlled with the 'white-space' property.
<p id="segment-normalization">
CSS does not define document segmentation rules. Segments can be
separated by a particular newline sequence (such as a line feed or
CRLF pair), or delimited by some other mechanism, such as the SGML
<code>RECORD-START</code> and <code>RECORD-END</code> tokens.
For CSS processing, each document language–defined segment break,
CRLF sequence (U+000D U+000A), carriage return (U+000D), and line feed (U+000A)
in the text is treated as a <dfn export>segment break</dfn>,
which is then interpreted for rendering as specified by the 'white-space' property.
<p class="note">Note that the document parser may have
not only normalized any <i>segment breaks</i>,
but also collapsed other space characters or
otherwise processed white space according to markup rules. Because CSS
processing occurs <em>after</em> the parsing stage, it is not possible
to restore these characters for styling. Therefore, some of the
behavior specified below can be affected by these limitations and
may be user agent dependent.</p>
<p class="note">Note that anonymous blocks consisting entirely of
<i>collapsible</i> <i>white space</i> are removed from the rendering tree.
Thus any such <i>white space</i> surrounding a block-level element is collapsed away.
See [[CSS21]] section
<a href="http://www.w3.org/TR/CSS21/visuren.html#anonymous">9.2.2.1</a></p>
<p>Control characters (Unicode class Cc) other than tab (U+0009), line feed
(U+000A), and carriage return (U+000D)
are ignored for the purpose of rendering.
(As required by [[!UNICODE]],
unsupported Default_ignorable characters must also be ignored for rendering.)
<h3 id="white-space-rules">
The White Space Processing Rules</h3>
<p>White space processing in CSS affects only
the <dfn export title="white space|white space characters| document white space|document white space characters">document white space characters</dfn>:
spaces (U+0020), tabs (U+0009), and <a href="#white-space-processing">segment breaks</a>.
<p class="note">
Note that the set of characters considered <i>document white space</i> (part of the document content)
and that considered syntactic white space (part of the CSS syntax)
are not necessarily identical.
However, since both include spaces (U+0020), tabs (U+0009), line feeds (U+000A), and carriage returns (U+000D)
most authors won't notice any differences.
<h4 id="white-space-phase-1">Phase I: Collapsing and Transformation</h4>
<p>For each inline (including anonymous inlines;
see [[CSS21]] section <a href="http://www.w3.org/TR/CSS21/visuren.html#anonymous">9.2.2.1</a>)
within an inline
formatting context, white space characters are handled as follows,
ignoring bidi formatting characters as if they were not there:</p>
<ul>
<li id="collapse"><p>If 'white-space' is set to
''white-space/normal'', ''nowrap'', or ''pre-line'',
white space characters are considered <dfn export title="collapsible white space|collapsible">collapsible</dfn>
and are processed by performing the following steps:</p>
<ol>
<li>All spaces and tabs immediately preceding or following a segment
break are removed.</li>
<li><i>Segment breaks</i> are transformed for
rendering according to the <a href="#line-break-transform">segment break transformation rules</a>.
</li>
<li>Every tab is converted to a space (U+0020).</li>
<li>Any space immediately following another collapsible space—even
one outside the boundary of the inline containing that space,
provided they are both within the same inline formatting
context—is collapsed to have zero advance width. (It is
invisible, but retains its <i>soft wrap opportunity</i>, if any.)</li>
</ol>
</li>
<li><p>If 'white-space' is set to ''pre-wrap'', any sequence of
spaces is treated as a sequence of non-breaking spaces. However,
a <i>soft wrap opportunity</i> exists at the end of the sequence.</p></li>
</ul>
<p>Then, the entire block is rendered. Inlines are laid out, taking bidi
reordering into account, and <i>wrapping</i> as specified by the
'white-space' property.</p>
<div class="example" id="egbidiwscollapse">
<p>The following example illustrates
the interaction of white-space collapsing and bidirectionality.
Consider the following markup fragment, taking special note of spaces
(with varied backgrounds and borders for emphasis and identification):
<pre><code><ltr>A<span class="egbidiwsaA"> </span><rtl><span class="egbidiwsbB"> </span>B<span class="egbidiwsaB"> </span></rtl><span class="egbidiwsbC"> </span>C</ltr></code></pre>
<p>where the <code><ltr></code> element represents a left-to-right embedding
and the <code><rtl></code> element represents a right-to-left embedding.
If the 'white-space' property is set to ''white-space/normal'',
the white-space processing model will result in the following:
<ul style="line-height:1.3">
<li>The space before the B (<span class="egbidiwsbB"> </span>)
will collapse with the space after the A (<span class="egbidiwsaA"> </span>).
<li>The space before the C (<span class="egbidiwsbC"> </span>)
will collapse with the space after the B (<span class="egbidiwsaB"> </span>).
</ul>
<p>This will leave two spaces,
one after the A in the left-to-right embedding level,
and one after the B in the right-to-left embedding level.
The text will then be ordered according to the Unicode bidirectional algorithm,
with the end result being:
<pre>A<span class="egbidiwsaA"> </span><span class="egbidiwsaB"> </span>BC</pre>
<p>Note that there will be two spaces between A and B,
and none between B and C.
This is best avoided by putting spaces outside the element
instead of just inside the opening and closing tags and, where practical,
by relying on implicit bidirectionality instead of explicit embedding levels.
</div>
<h4 id="line-break-transform">
Segment Break Transformation Rules</h4>
<p>When 'white-space' is ''pre'', ''pre-wrap'', or ''pre-line'',
<i>segment breaks</i> are not <i>collapsible</i>
and are instead transformed into a preserved line feed (U+000A).
<p>For other values of 'white-space', <i>segment breaks</i> are <i>collapsible</i>,
and are either transformed into a space (U+0020) or removed
depending on the context before and after the break:</p>
<ul>
<li>If the character immediately before or immediately after the segment
break is the zero-width space character (U+200B), then the break
is removed, leaving behind the zero-width space.
<li>Otherwise, if the East Asian Width property [[!UAX11]] of both
the character before and after the line feed is F, W, or H (not A),
and neither side is Hangul, then the segment break is removed.
<li>Otherwise, the segment break is converted to a space (U+0020).
</ul>
<p class="note">Note that the white space processing rules have already
removed any tabs and spaces after the segment break before these checks
take place.</p>
<p class="feedback issue">Comments on how well this would work in practice would
be very much appreciated, particularly from people who work with
Thai and similar scripts.
Note that browser implementations do not currently follow these rules
(although IE does in some cases transform the break).</p>
<h4 id="white-space-phase-2">Phase II: Trimming and Positioning</h4>
<p>As each line is laid out,</p>
<ol>
<li>A sequence of collapsible spaces at the beginning of a line is
removed.
<li>Each tab is rendered as a horizontal shift
that lines up the start edge of the next glyph with the next <i>tab stop</i>.
<dfn title="tab stop">Tab stops</dfn> occur at points that are multiples of the tab size
from the block's starting content edge.
The tab size is given by the 'tab-size' property.
<li>A sequence of <i>collapsible</i> spaces at the end of a line is removed.
<li>If spaces or tabs at the end of a line are non-collapsible but
have 'white-space' set to ''pre-wrap'' the UA may visually
collapse their character advance widths.
</ol>
<p>White space that was not removed or collapsed during the white space
processing steps is called <dfn>preserved</dfn> white space.</p>
<h3 id="tab-size-property">
Tab Character Size: the 'tab-size' property</h3>
<table class="propdef">
<tr>
<th>Name:</th>
<td><dfn>tab-size</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td><integer> | <length></td>
</tr>
<tr>
<th>Initial:</th>
<td>8</td>
</tr>
<tr>
<th>Applies to:</th>
<td>block containers</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>the specified integer or length made absolute</td>
</tr>
<tr>
<th>Animatable:
<td>as <a href="http://www.w3.org/TR/css3-transitions/#animtype-length">length</a>
<tr>
<th>Canonical order:
<td>N/A
</table>
<p>This property determines the tab size used to render preserved tab characters (U+0009).
8096
Integers represent the measure as multiples of the space character's advance width (U+0020).
Negative values are not allowed.
<h2 id="line-breaking">
Line Breaking and Word Boundaries</h2>
<p>When inline-level content is laid out into lines, it is broken across line boxes.
Such a break is called a <dfn>line break</dfn>.
When a line is broken due to explicit line-breaking controls,
or due to the start or end of a block,
it is a <dfn>forced line break</dfn>.
When a line is broken due to content <dfn title="wrapping|wrap">wrapping</dfn>
(i.e. when the UA creates unforced line breaks in order to fit the content within the measure),
it is a <dfn>soft wrap break</dfn>.
The process of breaking inline-level content into lines is called <dfn title="line-breaking-process">line breaking</dfn>.
<p>Wrapping is only performed at an allowed break point, called a <dfn export>soft wrap opportunity</dfn>.
<p>In most writing systems,
in the absence of hyphenation a <i>soft wrap opportunity</i> occurs only at word boundaries.
Many such systems use spaces or punctuation to explicitly separate words,
and <i>soft wrap opportunities</i> can be identified by these characters.
Scripts such as Thai, Lao, and Khmer, however,
do not use spaces or punctuation to separate words.
Although the zero width space (U+200B) can be used as an explicit word delimiter in these scripts,
this practice is not common.
As a result, a lexical resource is needed to correctly identify <i>soft wrap opportunities</i> in such texts.
<p>In several other writing systems, (including Chinese, Japanese, Yi, and sometimes also Korean)
a <i>soft wrap opportunity</i> is based on syllable boundaries, not word boundaries.
In these systems a line can break anywhere <em>except</em> between certain character combinations.
Additionally the level of strictness in these restrictions can vary with the typesetting style.</p>
<p>CSS does not fully define where <i>soft wrap opportunities</i> occur,
however some controls are provided to distinguish common variations.
<div class="note">
<p>Further information on line breaking conventions can be found in
[[JLREQ]] and [[JIS4051]] for Japanese,
[[ZHMARK]] for Chinese, and
in [[!UAX14]] for all scripts in Unicode.
<p class="feedback issue">Any guidance for appropriate references here would be
much appreciated.
</div>
<h3 id="line-break-details">
Line Breaking Details</h3>
<p>When determining <i>line breaks</i>:
<ul>
<li>Regardless of the 'white-space' value,
lines always break at each <i>preserved</i> forced break character:
for all values, line-breaking behavior defined for
the BK, CR, LF, CM, NL, and SG line breaking classes in [[!UAX14]]
must be honored.
<li>When 'white-space' allows wrapping,
line breaking behavior defined for the WJ, ZW, and GL line-breaking classes in [[!UAX14]]
must be honored.
<li>UAs that allow wrapping at punctuation other than spaces should prioritize breakpoints.
For example, if breaks after slashes are given a lower priority than spaces,
the sequence "check /etc" will never break between the "/" and the "e".
As long as care is taken to avoid such awkward breaks, allowing breaks at
appropriate punctuation other than spaces is recommended, as it results
in more even-looking margins, particularly in narrow measures.
The UA may use the width of the containing block, the text's language,
and other factors in assigning priorities.
<li>Out-of-flow elements do not introduce a <i>forced line break</i>
or <i>soft wrap opportunity</i> in the flow.
<li>The line breaking behavior of a replaced element or other atomic inline
is equivalent to that of the Object Replacement Character (U+FFFC)
and introduces a <i>soft wrap opportunity</i> both before and after itself.
For Web-compatibility, this rule take precedence over <code>WJ</code> and <code>GL</code> handling;
in terms of [[!UAX14]],
this shifts the <code>CB</code> rule (<a href="http://www.unicode.org/reports/tr14/#LB20"><code>LB20</code></a>)
immediately above the <code>WJ</code> and <code>GL</code> rules (<a href="http://www.unicode.org/reports/tr14/#LB11"><code>LB11</code></a>/<a href="http://www.unicode.org/reports/tr14/#LB12"><code>LB12</code></a>).
<li>For <i>soft wrap opportunities</i> created by characters that disappear at the line break (e.g. U+0020 SPACE),
properties on the element containing that character control the line breaking at that opportunity.
For <i>soft wrap opportunities</i> defined by the boundary between two characters,
the properties on the element containing the boundary control breaking.
<!-- http://lists.w3.org/Archives/Public/www-style/2008Dec/0043.html -->
<li>For <i>soft wrap opportunities</i> before the first or after the last character of a box,
the break occurs immediately before/after the box (at its margin edge)
rather than breaking the box between its content edge and the content.
<li>Line breaking in/around Ruby is defined in Ruby box and line breaking [[!CSS3RUBY]].
</ul>
<h3 id="word-break-property">
Breaking Rules for Letters: the 'word-break' property</h3>
<table class="propdef">
<tr>
<th>Name:</th>
<td><dfn>word-break</dfn></td>
</tr>
<tr>
<th><a href="#values">Value</a>:
<td>normal | keep-all | break-all</td>
</tr>
<tr>
<th>Initial:</th>
<td>normal</td>
</tr>
<tr>
<th>Applies to:</th>
<td>all elements</td>
</tr>
<tr>
<th>Inherited:</th>
<td>yes</td>
</tr>
<tr>
<th>Percentages:</th>
<td>N/A</td>
</tr>
<tr>
<th>Media:</th>
<td>visual</td>
</tr>
<tr>
<th>Computed value:</th>
<td>specified value</td>
</tr>
<tr>
<th>Animatable:
<td>no
<tr>
<th>Canonical order:
<td>N/A
</table>
<p>This property specifies <i>soft wrap opportunities</i> between letters,
i.e. where it is “normal” and permissible to break lines of text.
It does not affect rules governing the <i>soft wrap opportunities</i>
created by spaces and punctuation.
(See 'line-break' for controls affecting punctuation.)
<div class="example">
<p>For example, in some styles of CJK typesetting, English words are allowed
to break between any two letters, rather than only at spaces or hyphenation points;
this can be enabled with ''word-break:break-all''.
<div class="figure">
<img src="break-all.png" alt="A snippet of Japanese text with English in it. The word 'caption' is broken into 'capt' and 'ion' across two lines.">
<p class="caption">An example of English text embedded in Japanese
being broken at an arbitrary point in the word.
</div>
<p>As another example, Korean has two styles of line-breaking:
between any two Korean syllables (''word-break: normal'')
or, like English, mainly at spaces (''word-break: keep-all'').
<pre>각 줄의 마지막에 한글이 올 때 줄 나눔 기 /* break between syllables */
<!-- -->준을 “글자” 또는 “어절” 단위로 한다.</pre>
<pre>각 줄의 마지막에 한글이 올 때 줄 나눔 /* break only at spaces */
<!-- -->기준을 “글자” 또는 “어절” 단위로 한다.</pre>
</div>
<p class="note">
To enable additional break opportunities only in the case of overflow,
see 'overflow-wrap'.
<p>Values have the following meanings:</p>
<dl dfn-for=word-break dfn-type=value>
<dt><dfn>normal</dfn></dt>
<dd>Words break according to their customary rules,
as described <a href="#line-breaking">above</a>.
Korean, which commonly exhibits two different behaviors,
allows breaks between any two consecutive Hangul/Hanja.
<dt><dfn>break-all</dfn></dt>
<dd>Breaking is allowed within “words”:
in addition to ''word-break/normal'' <i>soft wrap opportunities</i>,
lines may break between any two <i>semantically-perceived letters</i>
(except where forbidden by the 'line-break' property).
Hyphenation is not applied. This option is used mostly in a context where
the text is predominantly using CJK characters with few non-CJK excerpts
and it is desired that the text be better distributed on each line.</dd>
<dt><dfn>keep-all</dfn></dt>
<dd>Breaking is forbidden within “words”:
implicit <i>soft wrap opportunities</i> between <i>semantically-perceived letters</i> are suppressed,
i.e. breaks are prohibited between pairs of letters
(regardless of 'line-break' settings)
except where opportunities exist due to dictionary-based breaking.
Otherwise this option is equivalent to ''word-break/normal''.
In this style, sequences of CJK characters do not break.
<p class=note>This is the other common behavior for Korean (which uses spaces between words),
and is also useful for mixed-script text where CJK snippets are mixed
into another language that uses spaces for separation.</dd>
</dl>
<p>Symbols that line-break the same way as letters of a particular category
are affected the same way as those letters.
<div class="example">
<p>Here's a mixed-script sample text:
<pre>这是一些汉字, and some Latin,<!--
--> و کمی نوشتن عربی, <!--
-->และตัวอย่างการเขียนภาษาไทย.</pre>
<p>The break-points are determined as follows (indicated by ‘·’):
<dl>
<dt>''word-break: normal''</dt>
<dd>
<pre>这·是·一·些·汉·字,·and·some·Latin,<!--
-->·و·کمی·نوشتن·عربی,·<!--
-->และ·ตัวอย่าง·การเขียน·ภาษาไทย.</pre>
<dt>''word-break: break-all''</dt>
<dd>
<pre>这·是·一·些·汉·字,·a·n·d·s·o·m·e·L·a·t·i·n,<!--
-->·و·ﮐ·ﻤ·ﻰ·ﻧ·ﻮ·ﺷ·ﺘ·ﻦ·ﻋ·ﺮ·ﺑ·ﻰ,·<!--
-->แ·ล·ะ·ตั·ว·อ·ย่·า·ง·ก·า·ร·เ·ขี·ย·น·ภ·า·ษ·า·ไ·ท·ย.</pre>
<dt>''word-break: keep-all''</dt>
<dd>
<pre>这是一些汉字,·and·some·Latin,<!--
-->·و·کمی·نوشتن·عربی,·<!--
-->แและ·ตัวอย่าง·การเขียน·ภาษาไทย.</pre>
</dl>