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<h1>CSS Text Module Level 4</h1>
<pre class='metadata'>
Shortname: css-text
Level: 4
Status: UD
Work Status: Exploring
Group: csswg
ED: http://dev.w3.org/csswg/css-text-4/
Editor: fantasai, Invited Expert, http://fantasai.inkedblade.net/contact
Editor: Koji Ishii, Invited Expert, kojiishi@gluesoft.co.jp
Editor: Alan Stearns, Adobe Systems, stearns@adobe.com
Abstract: This module defines properties for text manipulation and specifies their processing model. It covers line breaking, justification and alignment, white space handling, and text transformation.
</pre>
<h2 id="intro">
Introduction</h2>
Issue: Add final level 3 content
<h2 id="transforming">
Transforming Text</h2>
Issue: Add final level 3 content
<h2 id="white-space-processing">
White Space Processing</h2>
Issue: Add final level 3 tab-size and processing details
<h3 id="white-space-collapsing">
White Space Collapsing: the 'text-space-collapse' property</h3>
<p class="issue">This section is still under discussion and may change in future drafts.</p>
<pre class="propdef">
Name: text-space-collapse
Value: collapse | discard | preserve | preserve-breaks | preserve-spaces
Initial: collapse
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
<p class="issue">Need a property name</p>
This property declares whether and how
<a href="#white-space-processing">white space</a> inside the element is
collapsed. Values have the following meanings, which must be interpreted
according to the white space processing rules:
<dl dfn-for=text-space-collapse dfn-type=value>
<dt><dfn>collapse</dfn>
<dd>
This value directs user agents to collapse sequences of white space
into a single character
(or <a href="http://www.w3.org/TR/css-text/#line-break-transform">in some cases</a>, no character).
<dt><dfn>preserve</dfn>
<dd>
This value prevents user agents
from collapsing sequences of white space.
Line feeds are preserved as forced line breaks.
<dt><dfn>preserve-breaks</dfn>
<dd>
This value collapses white space as for ''collapse'', but preserves
line feeds as forced line breaks.
<dt><dfn>preserve-spaces</dfn>
<dd>
This value prevents user agents
from collapsing sequences of white space,
and converts tabs and line feeds to spaces.
(This value is intended to match the behavior
of xml:space="preserve" in SVG)
<dt><dfn>discard</dfn>
<dd>
This value directs user agents to "discard" all white space in the
element.
Issue: Does this preserve line break opportunities or no? Do we need a "hide" value?
</dl>
<div class="example">
The following style rules implement MathML's white space processing:
<pre>
@namespace m "http://www.w3.org/1998/Math/MathML";
m|* {
text-space-collapse: discard;
}
m|mi, m|mn, m|mo, m|ms, m|mtext {
text-space-collapse: trim-inner;
}
</pre>
</div>
<p class="issue">This section is still under discussion and may change in future drafts.</p>
<h3 id="white-space-trim">
White Space Trimming: the 'text-space-trim' property</h3>
<pre class="propdef">
Name: text-space-trim
Value: none | trim-inner || discard-before || discard-after
Initial: collapse
Applies to: all elements
Inherited: no
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property allows authors to specify trimming behavior
at the beginning and end of a box.
Values have the following meanings,
which must be interpreted according to the white space processing rules:
<dl dfn-for=text-space-trim dfn-type=value>
<dt><dfn>trim-inner</dfn>
<dd>
For block containers this value directs UAs to discard all whitespace
at the beginning of the element up to and including the last line feed
before the first non-white-space character in the element as well as
to discard all white space at the end of the element starting with the
first line feed after the last non-white-space character in the element.
For other elements this value directs UAs to discard all whitespace
at the beginning and end of the element.
<dt><dfn>discard-before</dfn>
<dd>
This value directs the UA to collapse all collapsible whitespace
immediately before the start of the element.
<dt><dfn>discard-after</dfn>
<dd>
This value directs the UA to collapse all collapsible whitespace
immediately after the end of the element.
</dl>
<div class="example">
<p>The following style rules render DT elements as a comma-separated list:
<pre>
dt { display: inline; }
dt + dt:before { content: ", "; text-space-collapse: discard-before; }
</pre>
</div>
<h2 id="line-breaking">
Line Breaking and Word Boundaries</h2>
Issue: Add final level 3 content
<h2 id="wrapping">
Text Wrapping</h2>
Text wrapping is controlled by the 'text-wrap',
'wrap-before',
'wrap-after',
'wrap-inside',
and overflow-wrap properties:
Issue: Add final level 3 overflow-wrap
<h3 id="text-wrap">
Text Wrap Settings: the 'text-wrap' property</h3>
<pre class="propdef">
Name: text-wrap
Value: normal | nowrap | balance
Initial: normal
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property specifies the mode for text wrapping.
Possible values:
<dl dfn-for=text-wrap dfn-type=value>
<dt><dfn>normal</dfn>
<dd>
Lines may break at allowed break points,
as determined by the line-breaking rules in effect.
Line breaking behavior defined
for the WJ, ZW, and GL line-breaking classes
in [[!UAX14]] must be honored.
<dt><dfn>nowrap</dfn>
<dd>
Lines may not break; text that does not fit within the block container
overflows it.
<dt><dfn>balance</dfn>
<dd>
Same as ''text-wrap/normal'' for inline-level elements.
For block-level elements that
contain line boxes as direct children,
line breaks are chosen to balance
the <a>inline-size</a> those line boxes consume,
if better balance than ''text-wrap/normal'' is possible.
This must not change the number of line boxes
the block would contain
if 'text-wrap' were set to ''text-wrap/normal''.
For balancing purposes,
the <a>inline-size</a> to consider includes
any length taken up
by floats that shorten the line box.
The <a>inline-size</a> to consider comes before
any adjustments for justification.
Line boxes are balanced when the standard deviation
from the average <a>inline-size</a> consumed
is reduced over the block
(including lines that end in a forced break).
The exact algorithm is UA-defined.
UAs may treat this value as ''text-wrap/normal'' if there are more than ten lines to balance.
</dl>
Regardless of the 'text-wrap' value,
lines always break at forced breaks:
for all values,
line-breaking behavior defined
for the BK, CR, LF, CM NL, and SG line breaking classes
in [[!UAX14]] must be honored.
UAs that allow breaks at punctuation other than spaces
should prioritize breakpoints.
For example,
if breaks after slashes have a lower priority than spaces,
the sequence “check /etc”
will never break between the ‘/’ and the ‘e’.
The UA may use the width of the containing block,
the text's language,
and other factors in assigning priorities.
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.
<!-- add a sample prioritization algorithm -->
<h3 id="wrap-before">
Inline breaks between boxes: the 'wrap-before'/'wrap-after' properties</h3>
<pre class="propdef">
Name: wrap-before, wrap-after
Value: auto | avoid | avoid-line | avoid-flex | line | flex
Initial: auto
Applies to: all elements
Inherited: no
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
These properties specify modifications to break opportunities
in line and flex line breaking
Possible values:
<dl dfn-for="wrap-before, wrap-after" dfn-type=value>
<dt><dfn>auto</dfn>
<dd>
Lines may break at allowed break points
before and after the element,
as determined by the line-breaking rules in effect.
<dt><dfn>avoid</dfn>
<dd>
Flex and line breaking is suppressed before/after the element:
the UA may only break before/after the element
if there are no other valid break points
in the line.
If the text breaks,
line-breaking restrictions are honored as for
''wrap-before/auto''.
<dt><dfn>avoid-line</dfn>
<dd>
Same as ''wrap-before/avoid'',
but only for line breaks.
<dt><dfn>avoid-flex</dfn>
<dd>
Same as ''wrap-before/avoid'',
but only for flex line breaks.
<dt><dfn>line</dfn>
<dd>
Force a line break before/after the element
if this is a valid line break point.
<dt><dfn>flex</dfn>
<dd>
Force a flex line break before/after the element
if this is a valid flex line break point
and the element is a flex item
in a multi-line flex container.
</dl>
<h3 id="wrap-inside">
Line breaks within boxes: the 'wrap-inside' property</h3>
<pre class="propdef">
Name: wrap-inside
Value: auto | avoid
Initial: auto
Applies to: all elements
Inherited: no
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
<dl dfn-for=wrap-inside dfn-type=value>
<dt><dfn>auto</dfn>
<dd>
Lines may break at allowed break points
within the element,
as determined by the line-breaking rules in effect.
<dt><dfn>avoid</dfn>
<dd>
Line breaking is suppressed within the element:
the UA may only break within the element
if there are no other valid break points in the line.
If the text breaks,
line-breaking restrictions are honored as for
''wrap-inside/auto''.
If elements with ''wrap-inside/avoid'' are nested
and the UA must break within these elements,
a break in an outer element must be used
before a break within an inner element may be used.
</dl>
<h4 id="example-avoid">
Example of using 'wrap-inside: avoid' in presenting a footer</h4>
<div class="example">
The priority of breakpoints can be set
to reflect the intended grouping of text.
Given the rules
<pre>
footer { wrap-inside: avoid; }
venue { wrap-inside: avoid; }
date { wrap-inside: avoid; }
place { wrap-inside: avoid; }
</pre>
and the following markup:
<pre>
<footer>
<venue>27th Internationalization and Unicode Conference</venue>
&#8226; <date>April 7, 2005</date> &#8226;
<place>Berlin, Germany</place>
</footer>
</pre>
In a narrow window the footer could be broken as
<pre>
27th Internationalization and Unicode Conference •
April 7, 2005 • Berlin, Germany
</pre>
or in a narrower window as
<pre>
27th Internationalization and Unicode
Conference • April 7, 2005 •
Berlin, Germany
</pre>
but not as
<pre>
27th Internationalization and Unicode Conference • April
7, 2005 • Berlin, Germany
</pre>
</div>
<h2 id="last-line-limits">
Last Line Minimum Length</h2>
<div class="issue">
See <a href="http://www.w3.org/mid/0BD85DFF-A147-44EF-B18A-FF03C3D67EF0@verou.me">thread</a>.
Issue is about requiring a minimum length for lines.
Common measures seem to be
<ul>
<li>At least as long as the text-indent.
<li>At least X characters.
<li>Percentage-based.
</ul>
Suggestion for value space is ''match-indent | <<length>> | <<percentage>>''
(with ''Xch'' given as an example to make that use case clear).
Alternately <<integer>> could actually count the characters.
It's unclear how this would interact with text balancing (above);
one earlier proposal had them be the same property
(with ''100%'' meaning full balancing).
People have requested word-based limits, but since this is really
dependent on the length of the word, character-based is better.
</div>
<h2 id="white-space-property">
Shorthand for White Space and Wrapping: the 'white-space' property</h2>
Diff needs to have the shorthand details
<h2 id="hyphenation">
Breaking Within Words</h2>
Issue: Add final level 3 content
<h3 id="hyphenate-character">
Hyphens: the 'hyphenate-character' property</h3>
<pre class="propdef">
Name: hyphenate-character
Value: auto | <string>
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property specifies strings that are shown between parts of
hyphenated words. The <dfn for=hyphenate-character>auto</dfn> value means that the user agent should
find an appropriate value, preferably from the same source as the
hyphenation dictionary. If a string is specified, it appears at
the end of the line before a hyphenation break.
<div class="example">
In Latin scripts, the hyphen character (U+2010) is often used to
indicate that a word has been split. Normally, it will not be
necessary to set it explicitly. However, this can easily be done:
<pre>
article { hyphenate-character: "\2010" }
</pre>
</div>
<p class="note">
Both hyphens triggered by automatic hyphenation and
hyphens triggered by soft hyphens are rendered according to
'hyphenate-character'.
<h3 id="hyphenate-size-limits">
Hyphenation Size Limit: the 'hyphenate-limit-zone' property</h3>
<pre class="propdef">
Name: hyphenate-limit-zone
Value: <percentage> | <length>
Initial: 0
Applies to: block containers
Inherited: yes
Percentages: refers to width of the line box
Computed value: as specified
Media: visual
</pre>
<p class="issue">Is 'hyphenate-limit-zone' a good name? Comments/suggestions?
This property specifies the maximum amount of unfilled space (before
justification) that may be left in the line box before hyphenation is
triggered to pull part of a word from the next line back up into the
current line.
<h3 id="hyphenate-char-limits">
Hyphenation Character Limits: the 'hyphenate-limit-chars' property</h3>
<pre class="propdef">
Name: hyphenate-limit-chars
Value: [ auto | <<integer>> ]{1,3}
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property specifies the minimum number of characters in a
hyphenated word. If the word does not meet the required minimum
number of characters in the word / before the hyphen / after the
hyphen, then the word must not be hyphenated. Nonspacing combining
marks (<span class="issue">Unicode class</span>) and intra-word
punctuation (Unicode classes P*) do not count towards the minimum.
If three values are specified, the first value is the required
minimum for the total characters in a word, the second value is
the minimum for characters before the hyphenation point, and
the third value is the minimum for characters after the hyphenation
point. If the third value is missing, it is the same as the second.
If the second value is missing,
then it is ''hyphenate-limit-chars/auto''.
The ''hyphenate-limit-chars/auto''
value means that the UA chooses a value that adapts to the current
layout.
<p class="note">Unless the UA is able to calculate a better value, it
is suggested that ''hyphenate-limit-chars/auto'' means 2 for before and after, and 5 for
the word total.
<div class="example">
In the example below, the minimum size of a hyphenated word is
left to the UA (which means it may vary depending on the language,
the length of the line, or other factors), but the minimum number
of characters before and after the hyphenation point is set to 3.
<pre>
p { hyphenate-limit-chars: auto 3; }
</pre>
</div>
<h3 id="hyphenate-line-limits">
Hyphenation Line Limits: the 'hyphenate-limit-lines' and 'hyphenate-limit-last' properties</h3>
<pre class="propdef">
Name: hyphenate-limit-lines
Value: no-limit | <integer>
Initial: no-limit
Applies to: block containers
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property indicates the maximum number of successive hyphenated
lines in an element. The ''no-limit'' value means that there is no limit.
In some cases, user agents may not be able to honor the specified value.
(See overflow-wrap.) It is not defined whether hyphenation introduced by
such emergency breaking influences nearby hyphenation points.
<pre class="propdef">
Name: hyphenate-limit-last
Value: none | always | column | page | spread
Initial: none
Applies to: block containers
Inherited: yes
Percentages: n/a
Computed value: as specified
Media: visual
</pre>
This property indicates hyphenation behavior at the end of elements,
column, pages and spreads. A spread is a set of two pages that are
visible to the reader at the same time. Values are:
<dl dfn-for=hyphenate-limit-lines dfn-type=value>
<dt><dfn>none</dfn>
<dd>
No restrictions imposed.
<dt><dfn>always</dfn>
<dd>
The last full line of the element, or the last line before any
column, page, or spread break inside the element should not be
hyphenated.
<dt><dfn>column</dfn>
<dd>
The last line before any column, page, or spread break inside
the element should not be hyphenated.
<dt><dfn>page</dfn>
<dd>
The last line before page or spread break inside the element
should not be hyphenated.
<dt><dfn>spread</dfn>
<dd>
The last line before any spread break inside the element should
not be hyphenated.
</dl>
<div class=example>
<pre>
p { hyphenate-limit-last: always }
div.chapter { hyphenate-limit-last: spread }
</pre>
</div>
<div class=example>
A paragraph may be formatted like this when 'hyphenate-limit-last: none' is set:
<pre>
This is just a
simple example
to show Antarc-
tica.
</pre>
With 'hyphenate-limit-last: always' one would get:
<pre>
This is just a
simple example
to show
Antarctica.
</pre>
</div>
<h2 id="alignment">
Alignment and Justification</h2>
Issue: Add final level 3 content
Add this value to text-align
<dl dfn-for=text-align dfn-type=value>
<dt><dfn><string></dfn></dt>
<dd>
The string must be a single character; otherwise the declaration must
be <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignored</a>.
When applied to a table cell, specifies the <dfn>alignment character</dfn>
around which the cell's contents will align. See
<a href="#character-alignment">below</a> for further details and
how this value combines with keywords.
</dl>
<h3 id="character-alignment">
Character-based Alignment in a Table Column</h3>
When multiple cells in a column have an alignment character specified,
the alignment character of each such cell in the column is centered along
a single column-parallel axis and the rest of the text in the column
shifted accordingly. (Note that the strings do not have to be the same
for each cell, although they usually are.)
<div class="example">
The following style sheet:
<pre>
TD { text-align: "." center }
</pre>
will cause the column of dollar figures in the following HTML table:
<pre class="html-example">
<TABLE>
<COL width="40">
<TR> <TH>Long distance calls
<TR> <TD> $1.30
<TR> <TD> $2.50
<TR> <TD> $10.80
<TR> <TD> $111.01
<TR> <TD> $85.
<TR> <TD> N/A
<TR> <TD> $.05
<TR> <TD> $.06
</TABLE>
</pre>
to align along the decimal point. The table might be rendered as
follows:
<pre>
+---------------------+
| Long distance calls |
+---------------------+
| $11.30 |
| $22.50 |
| $0.80 |
| $200567.01 |
| $85. |
| N/A |
| $.05 |
| $.06 |
+---------------------+
</pre>
</div>
A keyword value may be specified in conjunction with the <string>
value; if it is not given, it defaults to ''text-align/right''. This value is used:
<
AE0D
div>
<ul>
<li>
when character-based alignment is applied to boxes that are not table
cells.
<li>
when the text wraps to multiple lines (at unforced break points).
<li>
when a character-aligned cell spans more than one column. In this
case the keyword alignment value is used to determine which column's
axis to align with: the leftmost column for ''text-align/left'', the rightmost
column for ''text-align/right'' and ''text-align/center'', the startmost column for ''text-align/start'',
the endmost column for ''text-align/end''.
<li>
when the column is wide enough that the character alignment alone does
not determine the positions of its character-aligned contents. In this
case the keyword alignment of the first cell in the column with a
specified alignment character is used to slide the position of the
character-aligned contents to match the keyword alignment insofar as
possible without changing the width of the column.
For ''text-align/center'', the UA may center
the aligned contents using its extremes, center the alignment axis
itself (insofar as possible), or optically center the aligned contents
some other way (such as by taking a weighted average of the extent of
the cells' contents to either side of the axis).
</ul>
<p class="note">
Right alignment is used by default for character-based
alignment because numbering systems are almost all left-to-right even
in right-to-left writing systems, and the primary use case of
character-based alignment is for numerical alignment.
</p>
If the alignment character appears more than once in the text, the first
instance is used for alignment. If the alignment character does not appear
in a cell at all, the string is aligned as if the alignment character had
been inserted at the end of its contents.
Character-based alignment occurs before table cell width computation so
that auto width computations can leave enough space for alignment.
Whether column-spanning cells participate in the alignment prior to
or after width computation is undefined.
If width constraints on the cell contents prevent full alignment
throughout the column, the resulting alignment is undefined.
<h2 id="spacing">
Spacing</h2>
Issue: Add final level 3 word-spacing, letter-spacing
<h3 id="text-spacing-property">
Character Class Spacing: the 'text-spacing' property</h3>
<table class="propdef">
<tr>
<th>Name:
<td><dfn>text-spacing</dfn>
<tr>
<th>Value:
<td>normal | none |
[ trim-start | space-start ] ||
[ trim-end | space-end | allow-end ] ||
[ trim-adjacent | space-adjacent ] ||
no-compress ||
ideograph-alpha ||
ideograph-numeric ||
punctuation
<tr>
<th>Initial:
<td>normal
<tr>
<th>Applies to:
<td>block containers
<tr>
<th>Inherited:
<td>yes
<tr>
<th>Percentages:
<td>N/A
<tr>
<th>Media:
<td>visual
<tr>
<th>Computed value:
<td>specified value
</table>
This property controls spacing between adjacent characters
on the same line within the same inline formatting context
using a set of character-class-based rules.
Such spacing can either be created between or trimmed from the affected glyphs.
Values are defined as follows:
<dl dfn-for=text-spacing dfn-type=value>
<dt><dfn>normal</dfn>
<dd>
Specifies the baseline behavior,
equivalent to ''space-start allow-end trim-adjacent''.
<dt><dfn>none</dfn>
<dd>
Turns off all text-spacing features.
All fullwidth characters are set with full-width glyphs.
<dt><dfn>ideograph-alpha</dfn>
<dd>
Creates 1/4em extra spacing between runs of
<a>ideographs</a> and <a>non-ideographic letters</a>.
Note: A commonly used algorithm for determining this behavior is specified in [[JLREQ]].
<dt><dfn>ideograph-numeric</dfn>
<dd>
Creates 1/4em extra spacing between runs of
<a>ideographs</a> and <a>non-ideographic numerals</a> glyphs.
Note: A commonly used algorithm for determining this behavior is specified in [[JLREQ]].
<dt><dfn>punctuation</dfn>
<dd>
Creates extra non-breaking spacing around punctuation as required by language-specific typographic conventions.
In this level, if the element's content language is French,
narrow no-break space (U+202F) and no-break space (U+00A0) is inserted
where required by <a href="http://unicode.org/udhr/n/notes_fra.html">French typographic guidelines</a>.
Otherwise this value has no effect.
However future specifications may add automatic spacing behavior for other languages.
<dt><dfn>space-start</dfn>
<dd>
Set <a>fullwidth opening punctuation</a> with full-width glyphs (spaced)
at the start of each line.
<dt><dfn>trim-start</dfn>
<dd>
Set <a>fullwidth opening punctuation</a> with half-width glyphs (flush)
at the start of each line.
<dt><dfn>allow-end</dfn>
<dd>
Set <a>fullwidth closing punctuation</a> with half-width glyphs (flush)
at the end of each line
if it does not otherwise fit prior to justification;
otherwise set the punctuation with full-width glyphs.
<dt><dfn>space-end</dfn>
<dd>
Set <a>fullwidth opening punctuation</a> with full-width glyphs (spaced)
at the start of each line.
<dt><dfn>trim-end</dfn>
<dd>
Set <a>fullwidth closing punctuation</a> with half-width glyphs (flush)
at the end of each line.
<dt><dfn>space-adjacent</dfn>
<dd>
Set <a>fullwidth opening punctuation</a> with full-width glyphs (spaced)
when not at the start of the line.
Set <a>fullwidth closing punctuation</a> with full-width glyphs (spaced)
when not at the end of the line.
<dt><dfn>trim-adjacent</dfn>
<dd>
Collapse spacing between punctuation glyphs
<a href="#fullwidth-collapsing">as described below</a>.
<dt><dfn>no-compress</dfn>
<dd>
5DB3
Justification may not compress text-spacing.
(If this value is not specified, the justification process may reduce autospacing
except when the spacing is at the start or end of the line.)
Note: An example of compression rules is given for Japanese
in 3.8 Line Adjustment in [[JLREQ]].
</dl>
This property is additive with the 'word-spacing' and 'letter-spacing' properties.
That is, the amount of spacing contributed by the 'letter-spacing' setting (if any)
is added to the spacing created by 'text-spacing'.
The same applies to 'word-spacing'.
At element boundaries, the amount of extra spacing introduced between characters
is determined by and rendered within the innermost element that contains the boundary.
If the extra spacing is applied to a particular glyph,
then the spacing is determined by the innermost element containing that glyph.
Note: Values other than ''text-spacing/normal'', ''text-spacing/none'', ''trim-start'', ''trim-end'', and ''space-end''
are at-risk and may be dropped from this level of CSS.
They are defined here currently to help work out a complete design of this feature.
Support for this property is <em>optional</em>.
It is strongly recommended for UAs that wish to support CJK typography.
Issue: It was requested to add a value for doubling the space after periods.
<h4 id="fullwidth-collapsing">
Fullwidth Punctuation Collapsing</h4>
Typically, fullwidth characters have glyphs with the same advance width
as a standard Han character (e.g. 水 U+6C34).
However, many fullwidth punctuation glyphs only take up part of the fullwidth design space.
Thus such punctuation are not always set fullwidth.
Several values of 'text-spacing' allow the author to control
when such characters are set half-width (typically half the width of an ideograph)
and when they are set full-width.
In order to set the text as specified, the UA will need to either
<ul>
<li>
trim (kern) the blank half of the glyphs,
if they are given full-width and must be set half-width, or
<li>
add space to the glyphs,
if they are given half-width must be set full-width.
</ul>
Some fonts use proportional glyphs for fullwidth punctuation characters.
For such proportional glyphs, the given advance width is considered
simultaneously full-width and half-width: no space is added or removed.
<p class="note">
The advance width of a standard Han character
can be determined either from font metrics
such as the OpenType <code>ideo</code> and <code>idtp</code> baselines for the opposite writing mode,
or by taking the advance width of a Han character such as 水 U+6C34.
(The opposite writing mode must be used because some fonts are compressed
so that the characters are not square.)
More information on OpenType metrics can be found
<a href="http://www.microsoft.com/typography/otspec/baselinetags.htm#ideoembox">in the OpenType spec</a>.
Note that if 水 U+6C34, 卜 U+535C, and 一 U+4E00 do not all have the same advance width,
the font has proportional ideographs
and the fullwidth advance width cannot be reliably determined by measuring glyphs.
Unless 'text-spacing' is set to ''space-adjacent'' or ''text-spacing/none''
(or the font has proportional fullwidth punctuation glyphs),
the UA must collapse the space typically associated with such full width glyphs
as follows:
<ul>
<li>
Set <a>fullwidth opening punctuation</a> half-width if the previous character is
a <a>fullwidth opening punctuation</a>,
<a>fullwidth middle dot punctuation</a>,
or ideographic space (U+3000).
Else set it full-width.
<li>
Set <a>fullwidth closing punctuation</a> half-width if the next character is
a <a>fullwidth closing punctuation</a>,
<a>fullwidth middle dot punctuation</a>,
or ideographic space (U+3000).
Else set it full-width.
<li>
Set <a>fullwidth closing punctuation</a> followed by <a>fullwidth opening punctuation</a>
each at "3/4-width", i.e. halfway between full-width and half-width.
</ul>
<div class="example">
The following example table lists the punctuation pairs
affected by adjancent-pairs trimming.
It uses halfwidth equivalents to approximate the trimming effect.
<table class="data">
<caption>Demonstration of adjacent-pairs punctuation trimming</caption>
<thead>
<tr><th>Combination
<th>Sample Pair
<th>Looks Like
<tbody>
<tr><td scope=row>Opening—Opening
<td><tt lang="ja" class="char">〔</tt>+<tt lang="ja" class="char">（</tt>
<td><tt lang="ja" class="char">〔</tt><tt lang="ja" class="char half-r">(</tt>
<tr><td scope=row>Middle Dot—Opening
<td><tt lang="ja" class="char">・</tt>+<tt lang="ja" class="char">（</tt>
<td><tt lang="ja" class="char">・</tt><tt lang="ja" class="char">(</tt>
<tr><td scope=row>Closing—Opening
<td><tt lang="ja" class="char">〕</tt>+<tt lang="ja" class="char">（</tt>
<td><tt lang="ja" class="char">)<span class="quarter">　</span></tt><tt lang="ja" class="char"><span class="quarter">　</span>(</tt>
<tr><td scope=row>Ideographic Space—Opening
<td><tt lang="ja" class="char"> </tt>+<tt lang="ja" class="char">（</tt>
<td><tt lang="ja" class="char"> </tt><tt lang="ja" class="char">(</tt>
<tr><td scope=row>Closing—Closing
<td><tt lang="ja" class="char">）</tt>+<tt lang="ja" class="char">〕</tt>
<td><tt lang="ja" class="char">)</tt><tt lang="ja" class="char">〕</tt>
<tr><td scope=row>Closing—Middle Dot
<td><tt lang="j
3F91
a" class="char">）</tt>+<tt lang="ja" class="char">・</tt>
<td><tt lang="ja" class="char">)</tt><tt lang="ja" class="char">・</tt>
<tr><td scope=row>Closing—Ideographic Space
<td><tt lang="ja" class="char">）</tt>+<tt lang="ja" class="char"> </tt>
<td><tt lang="ja" class="char">)</tt><tt lang="ja" class="char"> </tt>
</table>
</div>
<h4 id="text-spacing-classes">
Text Spacing Character Classes</h4>
In the context of this property the following definitions apply:
Issue: Classes and Unicode code points need to be reviewed.
<dl>