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Showing content from https://www.w3.org/TR/2015/WD-css-text-4-20150922/ below:

CSS Text Module Level 4

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Add final level 3 tab-size and processing details

This section is still under discussion and may change in future drafts.

Need a property name

This property declares whether and how white space inside the element is collapsed. Values have the following meanings, which must be interpreted according to the white space processing rules:

collapse

This value directs user agents to collapse sequences of white space into a single character (or in some cases, no character).

preserve

This value prevents user agents from collapsing sequences of white space. Segment breaks are preserved as forced line breaks.

preserve-auto

This value preserves white space and segment breaks as for preserve. However, in order to match platform conventions for editable text fields, the UA may visually collapse the advance widths of preserved white space that occurs at the end of a line, and is not required to honor soft wrap opportunities between such spaces.

preserve-trim

This value preserves white space and segment breaks as for preserve. However, the UA must visually collapse to 0 the advance widths of all preserved white space that occur at the end of a line.

Note: the preserve-trim value is at risk.

The CSSWG would appreciate feedback on the use cases for this value, to evaluate whether this value is needed at all and if so, if trimming leading spaces could be needed as well.

preserve-breaks

This value collapses white space as for collapse, but preserves segment breaks as forced line breaks.

preserve-spaces

This value prevents user agents from collapsing sequences of white space, and converts tabs and segment breaks to spaces. (This value is intended to match the behavior of xml:space="preserve" in SVG.)

discard

This value directs user agents to “discard” all white space in the element.

Does this preserve line break opportunities or no? Do we need a "hide" value?

The following style rules implement MathML’s white space processing:

@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;
}

This section is still under discussion and may change in future drafts.

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:

trim-inner

For block containers this value directs UAs to discard all whitespace at the beginning of the element up to and including the last segment break 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 segment break 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.

discard-before

This value directs the UA to collapse all collapsible whitespace immediately before the start of the element.

discard-after

This value directs the UA to collapse all collapsible whitespace immediately after the end of the element.

The following style rules render DT elements as a comma-separated list:

dt { display: inline; }
dt + dt:before { content: ", "; text-space-collapse: discard-before; }

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Text wrapping is controlled by the text-wrap, wrap-before, wrap-after, wrap-inside, and overflow-wrap properties:

Add final level 3 overflow-wrap

This property specifies the mode for text wrapping. Possible values:

normal

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.

Should this be called wrap for consistency with flex-wrap?

nowrap

Lines may not break; text that does not fit within the block container overflows it.

balance

Same as normal for inline-level elements. For block-level elements that contain line boxes as direct children, line breaks are chosen to balance the inline-size those line boxes consume, if better balance than normal is possible. This must not change the number of line boxes the block would contain if text-wrap were set to normal.

For balancing purposes, the inline-size to consider includes any length taken up by floats that shorten the line box. The inline-size to consider comes before any adjustments for justification. Line boxes are balanced when the standard deviation from the average inline-size 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 normal if there are more than ten lines to balance.

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.

These properties specify modifications to break opportunities in line breaking (and flex line breaking [CSS3-FLEXBOX]). Possible values:

auto

Lines may break at allowed break points before and after the box, as determined by the line-breaking rules in effect.

avoid

Line breaking is suppressed immediately before/after the box: the UA may only break there if there are no other valid break points in the line. If the text breaks, line-breaking restrictions are honored as for auto.

avoid-line

Same as avoid, but only for line breaks.

avoid-flex

Same as avoid, but only for flex line breaks.

line

Force a line break immediately before/after the box if box is an inline-level box.

flex

Force a flex line break immediately before/after the box if the box is a flex item in a multi-line flex container.

Forced line breaks on inline-level boxes propagate upward through any parent inline boxes the same way forced breaks on block-level boxes propagate upward through any parent block boxes in the same fragmentation context. [CSS3-BREAK]

auto

Lines may break at allowed break points within the box, as determined by the line-breaking rules in effect.

avoid

Line breaking is suppressed within the box: the UA may only break within the box if there are no other valid break points in the line. If the text breaks, line-breaking restrictions are honored as for auto.

If boxes with avoid are nested and the UA must break within these boxes, a break in an outer box must be used before a break within an inner box may be used.

The priority of breakpoints can be set to reflect the intended grouping of text.

Given the rules

footer { wrap-inside: avoid; }
venue { wrap-inside: avoid; }
date { wrap-inside: avoid; }
place { wrap-inside: avoid; }

and the following markup:

<footer>
<venue>27th Internationalization and Unicode Conference</venue>
&#8226; <date>April 7, 2005</date> &#8226;
<place>Berlin, Germany</place>
</footer>

In a narrow window the footer could be broken as

27th Internationalization and Unicode Conference •
April 7, 2005 • Berlin, Germany

or in a narrower window as

27th Internationalization and Unicode
Conference • April 7, 2005 •
Berlin, Germany

but not as

27th Internationalization and Unicode Conference • April
7, 2005 • Berlin, Germany

See

. Issue is about requiring a minimum length for lines. Common measures seem to be

• At least as long as the text-indent.
• At least X characters.
• Percentage-based.

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.

This property is a shorthand for text-space-collapse, text-wrap, and text-space-trim.

Note: This shorthand combines both inheritable and non-inheritable properties. If this is a problem, please inform the CSSWG.

The following table gives the mapping of the values of the shorthand to its longhands.

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This property specifies strings that are shown between parts of hyphenated words. The auto 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.

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:

article { hyphenate-character: "\2010" }

Both hyphens triggered by automatic hyphenation and hyphens triggered by soft hyphens are rendered according to hyphenate-character.

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.

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 (Unicode class) 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 auto. The auto value means that the UA chooses a value that adapts to the current layout.

Unless the UA is able to calculate a better value, it is suggested that auto means 2 for before and after, and 5 for the word total.

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.

p { hyphenate-limit-chars: auto 3; }

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.

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:

none

No restrictions imposed.

always

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.

column

The last line before any column, page, or spread break inside the element should not be hyphenated.

page

The last line before page or spread break inside the element should not be hyphenated.

spread

The last line before any spread break inside the element should not be hyphenated.

p { hyphenate-limit-last: always }
div.chapter {  hyphenate-limit-last: spread }

A paragraph may be formatted like this when 'hyphenate-limit-last: none' is set:

This is just a
simple example
to show Antarc-
tica.

With 'hyphenate-limit-last: always' one would get:

This is just a
simple example
to        show
Antarctica.

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Add this value to text-align

<string>

The string must be a single character; otherwise the declaration must be ignored. When applied to a table cell, specifies the alignment character around which the cell’s contents will align. See below for further details and how this value combines with keywords.

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.)

The following style sheet:

TD { text-align: "." center }

will cause the column of dollar figures in the following HTML table:

<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>

to align along the decimal point. The table might be rendered as follows:

+---------------------+
| Long distance calls |
+---------------------+
|        $11.30       |
|        $22.50       |
|         $0.80       |
|    $200567.01       |
|        $85.         |
|        N/A          |
|          $.05       |
|          $.06       |
+---------------------+

A keyword value may be specified in conjunction with the <string> value; if it is not given, it defaults to right. This value is used:

• when character-based alignment is applied to boxes that are not table cells.
• when the text wraps to multiple lines (at unforced break points).
• 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 left, the rightmost column for right and center, the startmost column for start, the endmost column for end.
• 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 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).

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.

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.

Add final level 3 word-spacing, letter-spacing

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:

normal

Specifies the baseline behavior, equivalent to space-start allow-end trim-adjacent.

none

Turns off all text-spacing features. All fullwidth characters are set with full-width glyphs.

ideograph-alpha

Creates 1/4em extra spacing between runs of ideographs and non-ideographic letters.

Note: A commonly used algorithm for determining this behavior is specified in [JLREQ].

ideograph-numeric

Creates 1/4em extra spacing between runs of ideographs and non-ideographic numerals glyphs.

Note: A commonly used algorithm for determining this behavior is specified in [JLREQ].

punctuation

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 French typographic guidelines. Otherwise this value has no effect. However future specifications may add automatic spacing behavior for other languages.

space-start

Set fullwidth opening punctuation with full-width glyphs (spaced) at the start of each line.

trim-start

Set fullwidth opening punctuation with half-width glyphs (flush) at the start of each line.

allow-end

Set fullwidth closing punctuation 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.

space-end

Set fullwidth opening punctuation with full-width glyphs (spaced) at the start of each line.

trim-end

Set fullwidth closing punctuation with half-width glyphs (flush) at the end of each line.

space-adjacent

Set fullwidth opening punctuation with full-width glyphs (spaced) when not at the start of the line. Set fullwidth closing punctuation with full-width glyphs (spaced) when not at the end of the line.

trim-adjacent

Collapse spacing between punctuation glyphs as described below.

no-compress

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].

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 normal, 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 optional. It is strongly recommended for UAs that wish to support CJK typography.

It was requested to add a value for doubling the space after periods.

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

• trim (kern) the blank half of the glyphs, if they are given full-width and must be set half-width, or
• add space to the glyphs, if they are given half-width must be set full-width.

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.

The advance width of a standard Han character can be determined either from font metrics such as the OpenType ideo and idtp 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 in the OpenType spec. 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 none (or the font has proportional fullwidth punctuation glyphs), the UA must collapse the space typically associated with such full width glyphs as follows:

• Set fullwidth opening punctuation half-width if the previous character is a fullwidth opening punctuation, fullwidth middle dot punctuation, or ideographic space (U+3000). Else set it full-width.
• Set fullwidth closing punctuation half-width if the next character is a fullwidth closing punctuation, fullwidth middle dot punctuation, or ideographic space (U+3000). Else set it full-width.
• Set fullwidth closing punctuation followed by fullwidth opening punctuation each at "3/4-width", i.e. halfway between full-width and half-width.

The following example table lists the punctuation pairs affected by adjancent-pairs trimming. It uses halfwidth equivalents to approximate the trimming effect.

In the context of this property the following definitions apply:

Classes and Unicode code points need to be reviewed.

ideographs

Includes all typographic character units [CSS3TEXT] whose base character is listed below:

• All characters in the range of U+3041 to U+30FF, except those that belong to Unicode Punctuation [P*] category.
• CJK Strokes (U+31C0 to U+31EF).
• Katakana Phonetic Extensions (U+31F0 to U+31FF).
• All characters that belongs to Han Unicode Script Property [UAX24].

non-ideographic letters

Includes all typographic character units that belong to Unicode Letters [L*] and Mark [M*] category, except when any of the following conditions are met:

• is defined as ideograph.
• is categorized as East Asian Fullwidth (F) by [UAX11].
• is upright in vertical text flow using the text-orientation property or the text-combine-upright property.

non-ideographic numerals

Includes all typographic character units that belong to the Unicode Decimal Digit Number [Nd] category, except when any of the following conditions are met:

• is categorized as East Asian Fullwidth (F) by [UAX11].
• is upright in vertical text flow using the text-orientation property or the text-combine-upright property.

fullwidth opening punctuation

Includes any opening punctuation character (Unicode category Ps) that belongs to the CJK Symbols and Punctuation block (U+3000–U+303F) or is categorized as East Asian Fullwidth (F) by [UAX11]. Also includes LEFT SINGLE QUOTATION MARK (U+2018) and LEFT DOUBLE QUOTATION MARK (U+201C). When trimmed, the left (for horizontal text) or top (for vertical text) half is kerned.

fullwidth closing punctuation

Includes any closing punctuation character (Unicode category Pe) that belongs to the CJK Symbols and Punctuation block (U+3000–U+303F) or is categorized as East Asian Fullwidth (F) by [UAX11]. Also includes RIGHT SINGLE QUOTATION MARK (U+2019) and RIGHT DOUBLE QUOTATION MARK (U+201D). May also include fullwidth colon punctuation and/or fullwidth dot punctuation (see below). When trimmed, the right (for horizontal text) or bottom (for vertical text) half is kerned.

fullwidth middle dot punctuation

Includes MIDDLE DOT (U+00B7), HYPHENATION POINT (U+2027), and KATAKANA MIDDLE DOT (U+30FB). May also include fullwidth colon punctuation and/or fullwidth dot punctuation (see below).

fullwidth colon punctuation

Includes FULLWIDTH COLON (U+FF1A) and FULLWIDTH SEMICOLON (U+FF1B).

fullwidth dot punctuation

Includes IDEOGRAPHIC COMMA (U+3001), IDEOGRAPHIC FULL STOP (U+3002), FULLWIDTH COMMA (U+FF0C), FULLWIDTH FULL STOP (U+FF0E).

Whether fullwidth colon punctuation and fullwidth dot punctuation should be considered fullwidth closing punctuation or fullwidth middle dot punctuation depends on where in the glyph’s box the punctuation is drawn. If the punctuation is centered, then it should be considered middle dot punctuation. If the punctuation is drawn to one side (left in horizontal text, top in vertical text) and the other half is therefore blank then the punctuation should be considered closing punctuation and trimmed accordingly.

The UA must classify fullwidth colon punctuation and fullwidth dot punctuation under either the fullwidth closing punctuation category or the fullwidth middle dot punctuation category as appropriate. The UA may rely on language conventions and the writing mode (horizontal vs. vertical), and/or font information to determine this categorization. The UA may also add additional characters to any category as appropriate.

The following informative table summarizes language conventions for classifying fullwidth colon and dot punctuation:

Note that for Chinese fonts at least, the author observes that the standard convention is often not followed.

Japanese has three common start-edge typesetting schemes, which are distinguished by their handling of opening brackets.

Positioning of opening brackets at line head [JLREQ]

Assuming a UA style sheet of p { margin: 1em 0; }, CSS can achieve the Japanese typesetting styles with the following rules:

• Brackets flush with indent, flush with other lines (first scheme):

  p { /* Flush alignment */
    margin: 0;
    text-indent: 1em;
    text-spacing: trim-start;
  }
  

• Brackets preserve fullwidth spacing on all lines (second scheme):

  p { /* Fullwidth alignment */
    margin: 0;
    text-indent: 1em;
    text-spacing: normal;
  }
  

• Brackets hang in indent, flush with other lines (third scheme):

  p { /* Hanging alignment */
    margin: 0;
    text-indent: 1em;
    text-spacing: trim-start;
    hanging-punctuation: first;
  }
  

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Add final level 3 list, with Randy Edmunds and Florian Rivoal added

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words "for example" or are set apart from the normative text with class="example", like this:

Informative notes begin with the word "Note" and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

To avoid clashes with future CSS features, the CSS2.1 specification reserves a prefixed syntax for proprietary and experimental extensions to CSS.

Prior to a specification reaching the Candidate Recommendation stage in the W3C process, all implementations of a CSS feature are considered experimental. The CSS Working Group recommends that implementations use a vendor-prefixed syntax for such features, including those in W3C Working Drafts. This avoids incompatibilities with future changes in the draft.

Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

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