CSS Text Decoration Module Level 4

Editor’s Draft,

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This version:
https://drafts.csswg.org/css-text-decor-4/
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https://www.w3.org/TR/css-text-decor-4/
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Elika J. Etemad / fantasai (Invited Expert)
(Google)
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Abstract

This module contains the features of CSS relating to text decoration, such as underlines, text shadows, and emphasis marks.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, etc.

Status of this document

This is a public copy of the editors’ draft. It is provided for discussion only and may change at any moment. Its publication here does not imply endorsement of its contents by W3C. Don’t cite this document other than as work in progress.

Please send feedback by filing issues in GitHub (preferred), including the spec code “css-text-decor” in the title, like this: “[css-text-decor] …summary of comment…”. All issues and comments are archived. Alternately, feedback can be sent to the (archived) public mailing list www-style@w3.org.

This document is governed by the 2 November 2021 W3C Process Document.

1. Introduction

This subsection is non-normative.

This module covers text decoration, i.e. decorating the glyphs of the text once typeset according to font and typographic rules. (See [CSS-TEXT-3] and [CSS-FONTS-3].) Such features are traditionally used not only for purely decorative purposes, but also in some cases to show emphasis, for honorifics, and to indicate editorial changes such as insertions, deletions, and misspellings.

CSS Levels 1 and 2 only defined very basic line decorations (underlines, overlines, and strike-throughs) appropriate to Western typographical traditions. Level 3 of this module added the ability to change the color, style, position, and continuity of these decorations, and also introduced emphasis marks (traditionally used in East Asian typography), and shadows (which were proposed then deferred from Level 2). Level 4 introduces additional controls over these decorations.

1.1. Module Interactions

This module replaces and extends the text-decorating features defined in [CSS-TEXT-DECOR-3].

All of the properties in this module can be applied to the ::first-line and ::first-letter pseudo-elements.

1.2. Value Definitions

This specification follows the CSS property definition conventions from [CSS2] using the value definition syntax from [CSS-VALUES-3]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. Combination with other CSS modules may expand the definitions of these value types.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the CSS-wide keywords as their property value. For readability they have not been repeated explicitly.

1.3. Terminology

The terms typographic character unit (character), typographic letter unit (letter), and content language as used in this specification are defined in [CSS-TEXT-3]. Other terminology and concepts used in this specification are defined in [CSS2] and [CSS-WRITING-MODES-4].

2. Line Decoration: Underline, Overline, and Strike-Through

The following properties describe line decorations that are added to the content of an element. When specified on or propagated to an inline box, that box becomes a decorating box for that decoration, applying the decoration to all its box fragments. The decoration is then further propagated to any in-flow block-level boxes that split the inline (see CSS2.1 section 9.2.1.1). When specified on or propagated to a block container that establishes an inline formatting context, the decorations are propagated to an anonymous inline box that wraps all the in-flow inline-level children of the block container. When specified on or propagated to a ruby container, the decorations are propagated only to the ruby base. For all other box types, the decorations are propagated to all in-flow children.

Note that text decorations are not propagated to any out-of-flow descendants, nor to the contents of atomic inline-level descendants such as inline blocks and inline tables. They are also not propagated to inline children of inline boxes, although the decoration is applied to such boxes.

Underlines, overlines, and line-throughs are drawn only for non-replaced inline boxes, and are drawn across all text (including white space, letter spacing, and word spacing) except spacing (white space, letter spacing, and word spacing) at the beginning and end of a line. Atomic inlines, such as images and inline blocks, are not decorated. Margins, borders, and padding of the decorating box are always skipped, however the margins, border, and padding of descendant inline boxes are not.

Note that CSS 2.1 required skipping margins, borders, and padding always. In Level 3 and beyond, by default only the margins, borders, and padding of the decorating box are skipped. In the future CSS2.1 may be updated to match this new default.

Relatively positioning a descendant moves all text decorations applied to it along with the descendant’s text; it does not affect calculation of the decoration’s initial position on that line. The visibility property, text-shadow, filters, and other graphical transformations likewise also affect all text decorations applied to that box—including decorations propagated from an ancestor box—and do not affect the calculation of their initial positions or thicknesses. (In the case of line decorations drawn over an atomic inline or across the margins/borders/padding of a non-replaced inline box, they are analogously associated with the affected atomic inline / non-replaced inline box rather than with the decorating box.)

In the following style sheet and document fragment:
blockquote { text-decoration: underline; color: blue; }
em { display: block; }
cite { color: fuchsia; }
<blockquote>
 <p>
  <span>
   Help, help!
   <em> I am under a hat! </em>

   <cite> —GwieF </cite>
  </span>
 </p>
</blockquote>

...the underlining for the blockquote element is propagated to an anonymous inline box that surrounds the span element, causing the text "Help, help!" to be blue, with the blue underlining from the anonymous inline underneath it, the color being taken from the blockquote element. The <em>text</em> in the em block is also underlined, as it is in an in-flow block to which the underline is propagated. The final line of text is fuchsia, but the underline underneath it is still the blue underline from the anonymous inline element. Sample rendering of the above underline example This diagram shows the boxes involved in the example above. The rounded aqua line represents the anonymous inline element wrapping the inline contents of the paragraph element, the rounded blue line represents the span element, and the orange lines represent the blocks.

Note: Line decorations are propagated through the box tree, not through inheritance, and thus have no effect on descendants when specified on an element with display: contents.

2.1. Text Decoration Lines: the text-decoration-line property

Name: text-decoration-line
Value: none | [ underline || overline || line-through || blink ] | spelling-error | grammar-error
Initial: none
Applies to: all elements
Inherited: no (but see prose, above)
Percentages: n/a
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

This property, which is a sub-property of the text-decoration shorthand, specifies what line decorations, if any, are added by the element. Values other than text-decoration-line cause the element to originate the indicated text decorations, and to apply and propagate it as described above.

Note: Unless it is desired for the color, style, and thickness of the lines to be set by declarations lower in the cascade, it is safer to use the text-decoration shorthand instead of this longhand.

Values have the following meanings:

none
Neither produces nor inhibits text decoration.
underline
Each line of text is underlined.
overline
Each line of text has a line over it (i.e. on the opposite side from an underline).
line-through
Each line of text has a line through the middle.
blink
The text blinks (alternates between visible and invisible). Conforming user agents may simply not blink the text. Note that not blinking the text is one technique to satisfy checkpoint 3.3 of WAI-UAAG. This value is deprecated in favor of Animations [CSS3-ANIMATIONS].
spelling-error
This value indicates the type of text decoration used by the user agent to highlight spelling mistakes. Its appearance is UA-defined, and may be platform-dependent. It is often rendered as a red wavy underline.
grammar-error
This value indicates the type of text decoration used by the user agent to highlight grammar mistakes. Its appearance is UA defined, and may be platform-dependent. It is often rendered as a green wavy underline.

Note: In vertical writing modes, text-underline-position can cause the underline and overline to switch sides. This allows the position of underlines to key off of language-specific preferences automatically.

Since spelling-error and grammar-error decorations are entirely UA-defined, the UA may disregard the other sub-properties of text-decoration, as well any other properties typically affecting the appearance of line decorations (such as text-underline-position, color, stroke, or fill) when rendering these decorations. However, to the extent that honoring any of these properties would be meaningful and practical given the UA’s chosen rendering, the UA should apply them as modifications to its default styling.

2.2. Text Decoration Style: the text-decoration-style property

Name: text-decoration-style
Value: solid | double | dotted | dashed | wavy
Initial: solid
Applies to: all elements
Inherited: no
Percentages: n/a
Computed value: specified keyword
Canonical order: per grammar
Animation type: discrete

This property, which is a sub-property of the text-decoration shorthand, sets the line-drawing style of underlines, overlines, and line-throughs specified on the element with text-decoration-line, and affects all decorations originating from this element even if descendant boxes specify a different style.

Values have the same meaning as for the border-style properties [CSS-BACKGROUNDS-3]. wavy indicates a wavy line.

2.3. Text Decoration Color: the text-decoration-color property

Name: text-decoration-color
Value: <color>
Initial: currentcolor
Applies to: all elements
Inherited: no
Percentages: n/a
Computed value: computed color
Canonical order: per grammar
Animation type: by computed value type

This property, which is a sub-property of the text-decoration shorthand, sets the color of underlines, overlines, and line-throughs specified on the element with text-decoration-line, and affects all decorations originating from this element even if descendant boxes specify a different color.

2.4. Text Decoration Line Thickness: the text-decoration-thickness property

text-decoration-thickness

In all current engines.

Firefox70+Safari12.1+Chrome89+
Opera75+Edge89+
Edge (Legacy)NoneIENone
Firefox for AndroidNoneiOS Safari12.2+Chrome for Android89+Android WebView89+Samsung Internet15.0+Opera Mobile63+
Name: text-decoration-thickness
Value: auto | from-font | <length> | <percentage>
Initial: auto
Applies to: all elements
Inherited: no
Percentages: N/A
Computed value: specified keyword or absolute length
Canonical order: per grammar
Animation type: by computed value

This property, which is a sub-property of the text-decoration shorthand, sets the stroke thickness of underlines, overlines, and line-throughs specified on the element with text-decoration-line, and affects all decorations originating from this element even if descendant boxes specify a different thickness.

Values have the following meanings:

auto
The UA chooses an appropriate thickness for text decoration lines; see below.
from-font
If the first available font has metrics indicating a preferred underline width, use that width, otherwise behaves as auto.
<length>
Specifies the thickness of text decoration lines as a fixed length. The UA must floor the actual value at one device pixel.

Note: A length will inherit as a fixed value, and will not scale with the font.

<percentage>

Specifies the thickness of text decoration lines as a percentage of 1em. The UA must floor the actual value at one device pixel.

Note: A percentage will inherit as a relative value, and will therefore scale with changes in the font as it inherits.

2.4.1. Automatic Thickness of Text Decoration Lines

Some font formats (such as OpenType) can offer information about the appropriate thickness of a line decoration. The UA should use such font-based information when choosing auto line thicknesses wherever appropriate.

2.5. Determining the Position and Thickness of Line Decorations

This section is copied over from early drafts of Text Decoration Level 3. It is still under review, and needs integration with text-underline-offset and text-decoration-thickness.

Since line decorations can span elements with varying font sizes and vertical alignments, the best position for a line decoration is not necessarily the ideal position dictated by the decorating box. Instead, it’s calculated, per line, from all text decorated by the decorating box on that line, the considered text. However, descendants of the decorating box that are skipped due to text-decoration-skip, descendant inlines with text-decoration-skip: ink, and any descendants that do not participate in the decorating box’s inline formatting context are excluded from the set of considered text.

The line decoration positions are then calculated per line as follows (treating over-positioned underlines as over lines and under-positioned overlines as under lines):

over lines
Align the line decoration with respect to the highest over EM-box edge of the considered text.
alphabetic underlines
The alphabetic underline position is calculated by taking the ideal offset (from the alphabetic baseline) of each run of considered text, averaging those, and then using the lowest alphabetic baseline to actually position the line. (Alphabetic baselines can differ between baseline-aligned boxes if the dominant baseline is non-alphabetic.) To prevent superscripts and subscripts from throwing this position off-kilter, an inline with a non-initial computed vertical-align is treated as having the ideal underline position of its parent.
non-alphabetic under lines
Position the line decoration with respect to the lowest under EM-box edge of the considered text.
line-throughs
Line-throughs essentially use the same sort of averaging as for alphabetic underlines, but recompute the position when drawing across a descendant with a different computed font-size. (This ensures that the text remains effectively “crossed out” despite any font size changes.) For each run of considered text with the same font-size, compute an ideal position averaged from its font metrics. To prevent superscripts and subscripts from throwing this position off-kilter, an inline with a non-initial computed vertical-align is treated as having the ideal underline position of its parent. Position the portion of the line across each decorated fragment at that position.

For simplicity, line-throughs should draw over each element at that element’s preferred/averaged position. This can produce some undesirable jumpiness, but there doesn’t appear to be any way to avoid that which is correct in all instances, and all attempts are worryingly complex. What position should line-throughs adopt over elements that have a different font-size, but no considered text?

CSS does not define the thickness of line decorations. In determining the thickness of text decoration lines, user agents may consider the font sizes, faces, and weights of descendants to provide an appropriately averaged thickness.

The following figure shows the averaging for underline:

In the first rendering of the underlined text '1st a'
								 with 'st' as a superscript, both the '1st' and the 'a'
								 are rendered in a small font. In the second rendering,
								 the 'a' is rendered in a larger font. In the third, both
								 '1st' and 'a' are large.

In the three fragments of underlined text, the underline is drawn consecutively lower and thicker as the ratio of large text to small text increases.

Using the same example, a line-through would in the second fragment, instead of averaging the two font sizes, split the line-through into two segments:

In both cases, however, the superscript, due to the vertical-alignment shift, has no effect on the position of the line.

2.6. Text Decoration Shorthand: the text-decoration property

Name: text-decoration
Value: <'text-decoration-line'> || <'text-decoration-thickness'> || <'text-decoration-style'> || <'text-decoration-color'>
Initial: see individual properties
Applies to: see individual properties
Inherited: see individual properties
Percentages: see individual properties
Computed value: see individual properties
Animation type: see individual properties
Canonical order: per grammar

This property is a shorthand for setting text-decoration-line, text-decoration-thickness, text-decoration-style, and text-decoration-color in one declaration. Omitted values are set to their initial values.

The following example underlines unvisited links with a solid blue underline in CSS1 and CSS2 UAs and a navy dotted underline in CSS3 UAs.
:link {
  color: blue;
  text-decoration: underline;
  text-decoration: navy dotted underline; /* Ignored in CSS1/CSS2 UAs */
}

Note: The shorthand purposefully omits the text-underline-position property, which is a language/writing-system–dependent setting that keys off the content, so that it can cascade and inherit independently from the (uninherited) stylistic settings of the text-decoration shorthand.

2.7. Text Underline Position: the text-underline-position property

Name: text-underline-position
Value: auto | [ from-font | under ] || [ left | right ]
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: n/a
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

This property, which is not a sub-property of the text-decoration shorthand, sets the position of an underline with respect to the text, and defines its zero position for further adjustment by text-underline-offset. It affects all decorations originating from this element, even if descendant boxes specify a different position. It does not affect underlines specified by ancestor elements.

The following example styles modern Chinese, Japanese, and Korean texts with the appropriate underline positions in both horizontal and vertical text:
:root:lang(ja), [lang|=ja], :root:lang(ko), [lang|=ko] { text-underline-position: under right; }
:root:lang(zh), [lang|=zh] { text-underline-position: under left; }

If left or right is specified alone, auto is also implied. Values have the following meanings:

auto
The user agent may use any algorithm to determine the underline’s position; however it must be placed at or under the alphabetic baseline.

Note: It is suggested that the default underline position be close to the alphabetic baseline, unless that would either cross subscripted (or otherwise lowered) text or draw over glyphs from Asian scripts such as Han or Tibetan for which an alphabetic underline is too high: in such cases, shifting the underline lower or aligning to the em box edge as described for under may be more appropriate.

In a typical Latin font, the underline is positioned slightly
				         below the alphabetic baseline, leaving a gap between the line
				         and the bottom of most Latin letters, but crossing through
				         descenders such as the stem of a 'p'.

A typical “alphabetic” underline is positioned just below the alphabetic baseline

from-font
If the first available font has metrics indicating a preferred underline offset, use that offset, otherwise behaves as auto.
under
The underline is positioned under the element’s text content. In this case the underline usually does not cross the descenders. (This is sometimes called “accounting” underline.) This value can be combined with left or right if a particular side is preferred in vertical typographic modes.
Because text-underline-position inherits, and is not reset by the text-decoration shorthand, the following example switches the document to use under underlining, which can be more appropriate for writing systems with long, complicated descenders. It is also often useful for mathematical or chemical texts that use many subscripts.
:root { text-underline-position: under; }

Note: The under value does not guarantee that the underline will not conflict with glyphs, as some fonts have descenders or diacritics that extend below the font’s descent metrics.

left
In vertical typographic modes, the underline is aligned as for under, except it is always aligned to the left edge of the text. If this causes the underline to be drawn on the "over" side of the text, then an overline also switches sides and is drawn on the "under" side.
right
In vertical typographic modes, the underline is aligned as for under, except it is always aligned to the right edge of the text. If this causes the underline to be drawn on the "over" side of the text, then an overline also switches sides and is drawn on the "under" side.
In mixed Japanese-Latin vertical text, 'text-underline-position: left'
					          places the underline on the left side of the text. In mixed Japanese-Latin vertical text, 'text-underline-position: right'
					          places the underline on the right side of the text.
left right

In vertical typographic modes, the text-underline-position values left and right allow placing the underline on either side of the text. (In horizontal typographic modes, both values are treated as auto.)

2.8. Text Underline Offset: the text-underline-offset property

text-underline-offset

In all current engines.

Firefox70+Safari12.1+Chrome87+
Opera73+Edge87+
Edge (Legacy)NoneIENone
Firefox for AndroidNoneiOS Safari12.2+Chrome for Android87+Android WebView87+Samsung Internet14.0+Opera MobileNone
Name: text-underline-offset
Value: auto | <length> | <percentage>
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: N/A
Computed value: specified keyword or absolute length
Canonical order: per grammar
Animation type: by computed value

This property, which is not a sub-property of the text-decoration shorthand, sets the offset of underlines from their zero position. Positive offsets represent distances outward from the text; negative offsets inward. It affects all decorations originating from this element, even if descendant boxes specify a different position. It does not affect underlines specified by ancestor elements.

Values have the following meanings:

auto

The UA chooses an appropriate offset for underlines.

However, this offset must be zero if the computed value of text-underline-position is from-font and the UA was able to extract an appropriate metric to use from the font.

<length>

Specifies the offset of underlines as a fixed length.

Note: A length will inherit as a fixed value, and will not scale with the font.

<percentage>

Specifies the offset of underlines as a percentage of 1em.

Note: A percentage will inherit as a relative value, and will therefore scale with changes in the font as it inherits.

When the value of the text-decoration-line property is either spelling-error or grammar-error, the UA may ignore the value of text-underline-position.

2.8.1. Underline Offset Origin (Zero Position)

The zero position of the underline depends on the value of text-underline-position as detailed below.

Interaction of text-underline-position and text-underline-offset
text-underline-position Zero Position Positive Direction
auto alphabetic baseline under
from-font position specified by the font metrics, falling back to alphabetic baseline under
under text-under edge under
left text-under (left) edge under
right text-over (right) edge over

The underline is aligned to the outside of the specified position (extending its thickness in the positive direction only).

Any automatic adjustments made to accommodate descendant content are maintained; the text-underline-offset is in addition to those.

2.8.2. Using Font Metrics for Automatic Positioning

Some font formats (such as OpenType) can offer information about the appropriate position of a line decoration. The UA should use such font-based information in its choice of auto offset wherever appropriate, and must use such information when from-font is specified for text-underline-position.

Note: Typically, OpenType font metrics give the position of an alphabetic underline; in some cases (especially in CJK fonts), it gives the position of a under left underline. (In this case, the font’s underline metrics typically touch the bottom edge of the em box). The UA may but is not required to correct for incorrect font metrics.

2.9. Text Decoration Line Uniformity

The exact position and thickness of line decorations depends on the values of text-underline-position, text-underline-offset, and text-decoration-thickness as defined above, and is otherwise UA-defined. However, for underlines and overlines the UA must use a single thickness and position on each line for the decorations deriving from a single decorating box.

A single underline drawn under varying font sizes and vertical positions must be a single line. vs. Drawing multiple line segments, each with the position and thickness appropriate to the decorated text, is incorrect.

Correct and incorrect rendering of <u>A<sup>B</sup><big>C</big>D</u>

Note, since line decorations can span elements with varying font sizes and vertical alignments, the best position for a line decoration is not necessarily the ideal position dictated by the decorating box. For example, an overline positioned to a small font will effectively become a line-through if the element contains text in a significantly larger font-size. Even for underlines, if the text is not aligned to the alphabetic baseline (for example, in vertical typesetting styles, text is aligned by its central baseline by default [CSS-WRITING-MODES-4]) an underline will cut through descendant text of a larger font-size. UA consideration of descendant content will therefore result in better typography.

Due to the central baseline alignment of vertical text, a left-side underline on small vertical text will cut through the text of a child with a larger font size. The underline is not allowed to be broken, but adjusting its position further to the left properly accommodates all of the underlined text.

UAs must adjust line positions to match the shifted metrics of decorating boxes shifted with vertical-align values other than baseline [CSS2] or subscripted/superscripted via font-variant-position [CSS-FONTS-3], but must not adjust the line position or thickness in response to descendants of a decorating box that are so styled (even though it may adjust the position to accommodate descendants that are not so styled, such as those merely typeset in a different font size as noted above). This allows superscripts and subscripts to be properly decorated (underlined, struck through, etc.) but prevents them from distorting or breaking the positioning of such decorations on their ancestors.

An underline for just the superscript 'st' in '1st' is drawn just below the superscript,
		             whereas an underline for the entire text is drawn at the appropriate position for full-size text.

Example of underline applied to superscripted text vs. underline applied to text containing a superscript

2.10. Text Decoration Line Continuity: the text-decoration-skip shorthand and its sub-properties

text-decoration-skip

In only one current engine.

FirefoxNoneSafari12.1+Chrome57–64
Opera44–50EdgeNone
Edge (Legacy)NoneIENone
Firefox for AndroidNoneiOS Safari12.2+Chrome for Android57–64Android WebView57–64Samsung Internet7.0–9.0Opera Mobile43–46

The CSSWG resolved to be split skipping functionality into individual properties along the lines of text-decoration-skip-ink, to improve its cascading behavior. See discussion and resolution. This section is a rough draft and has not yet been vetted by the CSSWG

Name: text-decoration-skip
Value: none | auto
Initial: See individual properties
Applies to: all elements
Inherited: yes
Percentages: N/A
Computed value: See individual properties
Canonical order: per grammar
Animation type: discrete

The text-decoration-skip property and its sub-properties (text-decoration-skip-self, text-decoration-skip-box, text-decoration-skip-inset, text-decoration-skip-spaces, text-decoration-skip-ink) control interruptions in line decorations for which the element or an ancestor is the decorating box. The none value sets all sub-properties to none, and the auto value sets all sub-properties to their initial values.

Is this none definition Web-compatible? Do we also need to add an ink value for Web-compat?

Note that these properties inherit and that descendant elements can have a different setting.

The following addition is made to the default UA stylesheet for HTML:

ins, del { text-decoration-skip: none; }

When the value of the text-decoration-line property is either spelling-error or grammar-error, the UA may ignore any or all of these properties.

2.10.1. Skipping Spaces: the text-decoration-skip-self property

Name: text-decoration-skip-self
Value: none | objects
Initial: objects
Applies to: all elements
Inherited: yes
Percentages: N/A
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

The CSSWG resolved to split text-decoration-skip into sub-properties, but this value set has not yet been vetted by the CSSWG.

This property specifies whether any text decoration lines drawn by its ancestors are propagated to or drawn across the element. Values have the following meanings:

none
Skip nothing: line decorations from ancestor decorating boxes are propagated to or drawn across this box, as appropriate.
objects
Skip this element (its entire margin box) if it is an atomic inline (such as an image or inline-block).

2.10.2. Skipping Spaces: the text-decoration-skip-box property

Name: text-decoration-skip-box
Value: none | all
Initial: none
Applies to: all elements
Inherited: yes
Percentages: N/A
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

The CSSWG resolved to split text-decoration-skip into sub-properties, but this value set has not yet been vetted by the CSSWG.

This property specifies what parts of the element’s box area any text decoration affecting the element must skip over. It controls only text decoration lines drawn by its ancestors. Values have the following meanings:

none
Skip nothing: line decorations from ancestor decorating boxes are drawn from margin edge to margin edge.
all
When drawing text decoration lines applied to an ancestor decorating box, skip over the box’s own margin, border, and padding areas and only draw line decorations within its content area.

This value only has an effect for decorations imposed by an ancestor; a decorating box never draws over its own box decoration.

2.10.3. Inset Edges: the text-decoration-skip-inset property

Name: text-decoration-skip-inset
Value: none | auto
Initial: none
Applies to: all elements
Inherited: yes
Percentages: N/A
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

The CSSWG resolved to split text-decoration-skip into sub-properties, but this value set has not yet been vetted by the CSSWG.

This property specifies what parts of the element’s box area any text decoration affecting the element must skip over. It controls all text decoration lines drawn by the element, but not any text decoration lines drawn by its ancestors. Values have the following meanings:

none
Skip nothing: text-decoration is drawn from box edge to box edge.
auto
The UA must place the start and end of the line inwards slightly from the content edge of the decorating box so that, e.g. two underlined elements side-by-side do not appear to have a single underline. The size of the inset is up to the user agent (e.g. half a line thickness) but must not be zero. (This is important in Chinese, where underlining is a form of punctuation.)

An underline below a series of Chinese characters has a gap between two adjacent underlining elements.

text-decoration-skip-inset: auto for <u>石井</u><u>艾俐俐</u>

This might want to be a standalone property rather than part of the text-decoration-skip set. See also Issue 4557, about controlling the line length explicitly.

2.10.4. Skipping Spaces: the text-decoration-skip-spaces property

Name: text-decoration-skip-spaces
Value: none | all | [ start || end ]
Initial: start end
Applies to: all elements
Inherited: yes
Percentages: N/A
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

Should the initial value be none for Web-compat? If not, INS and DEL at least should be assigned none in the UA default stylesheet. See also Issue 4653.

This property specifies whether text decoration skips any spaces. It controls all text decoration lines drawn by the element and also any text decoration lines drawn by its ancestors. Values have the following meanings:

none
Spacers are not skipped. They are decorated just like any other character.
all
Skip all spacers, plus any adjacent letter-spacing or word-spacing.
start
Skip all spacers, plus any adjacent letter-spacing or word-spacing, when located at the start of the line.
end
Skip all spacers, plus any adjacent letter-spacing or word-spacing, when located at the end of the line.

For the purpose of this property, a spacer is any typographic character unit with the Unicode White_Space property [UAX44] except U+202F NARROW NO-BREAK SPACE, or any word separator.

2.10.5. Skipping Glyphs: the text-decoration-skip-ink property

text-decoration-skip-ink

In all current engines.

Firefox70+Safari15.4+Chrome64+
Opera50+Edge79+
Edge (Legacy)NoneIENone
Firefox for AndroidNoneiOS Safari15.4+Chrome for Android64+Android WebView64+Samsung Internet9.0+Opera Mobile46+
Name: text-decoration-skip-ink
Value: auto | none | all
Initial: auto
Applies to: all elements
Inherited: yes
Percentages: N/A
Computed value: specified keyword
Canonical order: per grammar
Animation type: discrete

This property controls how overlines and underlines are drawn when they cross over a glyph. It affects all decorations originating from this element even if descendant boxes specify a different style.

When enabled, decoration lines skip over where glyphs are drawn: interrupt the decoration line to let the shape of the text show through where the text decoration would otherwise cross over a glyph. The UA must also skip a small distance to either side of the glyph outline.

An alphabetic underline through Myanmar text skips around descenders and the vertical strokes of combining characters that drop below the alphabetic baseline.

Skipping Glyph Ink

Ideographic scripts do not want to skip when auto. How can we define this behavior? Are there more scripts wanting not to skip? Need some normative text describe how auto works. See telcon minutes, alreq#86, csswg#1288

This property only applies to overlines and underlines; line-throughs are always continuous.

auto
UAs may interrupt underlines and overlines where the line would cross glyph ink and to some distance to either side of the glyph outline. UAs should consider the script of the text (see note below) when determining whether to apply ink-skipping behavior to a given range of content.
all
UAs must interrupt underlines and overlines where the line would cross glyph ink and to some distance to either side of the glyph outline.
none
UA must draw continuous underlines and overlines, without interruptions when they cross over a glyph.
Note: Implementation experience shows that ink-skipping behavior often produces undesirable results when underlined text includes ideographic characters, as the underline position (depending on the font and user agent involved) often clashes with almost all the glyphs, such that only occasional fragments of the line remain to be rendered.

In principle, this could be resolved by authors using text-underline-position: under (or possibly text-underline-offset) to move the underline to a lower position that does not clash with the glyphs, but this is not always feasible, even if the user agent supports these properties and the author is aware of their potential. In particular, when a page contains arbitrary user-generated content, the author responsible for the design may not know whether CJK content will be present. And with mixed-script content, an underline position designed to work well for CJK content may look bad if the majority of the text is non-CJK.

Therefore, when auto is in effect, a UA that implements ink-skipping should refrain from doing so in CJK contexts. (Authors who do want ink-skipping applied to CJK content can use the always value to explicitly request this.)

Primarily, this means not applying ink-skipping for characters whose Unicode Script property is any of the CJK scripts Han, Hiragana, Katakana, Bopomofo, or Hangul, or for characters whose Script property is Inherited or Common, and whose ScriptExtensions property includes one or more of the CJK scripts.

In addition, characters with a Unicode script property of Common and Inherited (primarily generic punctuation and symbols) need to be considered, as these may be used as part of a run of CJK-script content, and it is desirable to treat all text within a given script run in a consistent way. Therefore, the UA should resolve the text into script runs as described in the “Implementation Notes” of [UAX24] “Unicode Script Property”, in particular subsections 5.1 and 5.2. After applying the heuristics described there (or a similar analysis of scripts), the UA should disable ink-skipping for all ranges of text that are determined to be in a CJK script.

Are there other (non-CJK) scripts where it would be preferable to disable ink-skipping by default (when auto is in effect)? Perhaps Yi? Arabic? (See also discussion in Issue 1288.)

2.10.6. Shaping Interruptions

When the UA interrupts underlines or overlines at glyph boundaries, the shape of the line at that boundary should follow the shape of the glyph.

Note, this specification intentionally does not mandate a particular method for “following the shape” of the glyph so that UAs can take appropriate measures to handle aesthetic and performance considerations. For example, a UA could assume square line endings below a certain size threshold for performance reasons; or use trapezoidal endings to approximate curves, especially on thinner line decorations. In terms of aesthetic considerations, the UA might also consider what happens when the glyph boundary intersects only part of the line thickness or is slanted close to the horizontal—following the curve exactly could result in typographically-awkward wisps of underline. Whether to show the line within enclosed areas of a glyph is yet another consideration.
Take, for example, the word “goal” with an underline striking through the bottom loop of the “g”.
			            Depending on the position and thickness of the underline,
			            we might see the entire thickness of the underline, or only part of it within the “g”.
			            This example shows a masked-out underline in two positions.
			            In the left pair the underline passes through the center of the bowl of the “g”:
			            the full thickness of the underline shows through the center,
			            filling it.
			            In the right pair the underline is slightly lower,
			            and thus the portion of the underline within the “g” can only show a partial thickness.

Hiding the portion of the underline within the bowl gives a cleaner look to the type, while the curved ends of the underline outside it suggest the continuity of the underline through the letter by hugging its outer contour.

3. Additional Controls for Emphasis Marks

East Asian documents traditionally use small symbols next to each glyph to emphasize a run of text. For example:

Example of emphasis in Japanese appearing over the text

Accent emphasis (shown in blue for clarity) applied to Japanese text

The text-emphasis shorthand, and its text-emphasis-style and text-emphasis-color longhands, can be used to apply such marks to the text. The text-emphasis-position property, which inherits separately, allows setting the emphasis marks’ position with respect to the text.

See also issue about continuity in size/position.

3.1. Emphasis Mark Style: the text-emphasis-style property

Name: text-emphasis-style
Value: none | [ [ filled | open ] || [ dot | circle | double-circle | triangle | sesame ] ] | <string>
Initial: none
Applies to: text
Inherited: yes
Percentages: n/a
Computed value: the keyword none, a pair of keywords representing the shape and fill, or a string
Canonical order: per grammar
Animation type: discrete

This property applies emphasis marks to the element’s text. Values have the following meanings:

none
No emphasis marks.
filled
The shape is filled with solid color.
open
The shape is hollow.
dot
Display small circles as marks. The filled dot is U+2022 '•', and the open dot is U+25E6 '◦'.
circle
Display large circles as marks. The filled circle is U+25CF '●', and the open circle is U+25CB '○'.
double-circle
Display double circles as marks. The filled double-circle is U+25C9 '◉', and the open double-circle is U+25CE '◎'.
triangle
Display triangles as marks. The filled triangle is U+25B2 '▲', and the open triangle is U+25B3 '△'.
sesame
Display sesames as marks. The filled sesame is U+FE45 '﹅', and the open sesame is U+FE46 '﹆'.
<string>
Display the given string as marks. Authors should not specify more than one character in <string>. The UA may truncate or ignore strings consisting of more than one grapheme cluster.

If a shape keyword is specified but neither of filled nor open is specified, filled is assumed. If only filled or open is specified, the shape keyword computes to circle in horizontal typographic modes and sesame in vertical typographic modes.

The marks should be drawn using the element’s font settings with the addition of the ruby feature and the size scaled down 50%. However, since not all fonts have all these glyphs, and some fonts use inappropriate sizes for emphasis marks in these code points, the UA may opt to use a font known to be good for emphasis marks, or the marks may instead be synthesized by the UA. Marks must remain upright in vertical typographic modes: like CJK characters, they do not rotate to match the writing mode. The orientation of marks in horizontal typographic modes of vertical writing modes is undefined in this level (but may be defined in a future level if definitive use cases arise).

Note: One example of good fonts for emphasis marks is Adobe’s open source Kenten Generic OpenType Font, which is specially designed for the emphasis marks.

The marks are drawn once for each typographic character unit. However, emphasis marks are not drawn for:

Note: Control over which characters are marked will be added in Level 4. (The list of punctuation may also be further refined, particularly for non-CJK punctuation.)

3.2. Emphasis Mark Color: the text-emphasis-color property

Name: text-emphasis-color
Value: <color>
Initial: currentcolor
Applies to: text
Inherited: yes
Percentages: n/a
Computed value: computed color
Canonical order: per grammar
Animation type: by computed value type

This property specifies the foreground color of the emphasis marks.

Note: currentcolor keyword computes to itself and is resolved to the value of color after inheritance is performed. This means text-emphasis-color by default matches the text color even as color changes across elements.

3.3. Emphasis Mark Shorthand: the text-emphasis property

Name: text-emphasis
Value: <'text-emphasis-style'> || <'text-emphasis-color'>
Initial: see individual properties
Applies to: see individual properties
Inherited: see individual properties
Percentages: see individual properties
Computed value: see individual properties
Animation type: see individual properties
Canonical order: per grammar

This property is a shorthand for setting text-emphasis-style and text-emphasis-color in one declaration. Omitted values are set to their initial values.

Note that text-emphasis-position is not reset in this shorthand. This is because typically the shape and color vary, but the position is consistent for a particular language throughout the document. Therefore the position should inherit independently.

3.4. Emphasis Mark Position: the text-emphasis-position property

Name: text-emphasis-position
Value: [ over | under ] && [ right | left ]?
Initial: over right
Applies to: text
Inherited: yes
Percentages: n/a
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

This property describes where emphasis marks are drawn at. If [ right | left ] is omitted, it defaults to right. The values have following meanings:

over
Draw marks over the text in horizontal typographic modes.
under
Draw marks under the text in horizontal typographic modes.
right
Draw marks to the right of the text in vertical typographic modes.
left
Draw marks to the left of the text in vertical typographic modes.

Emphasis marks are drawn exactly as if each character was assigned the mark as its ruby annotation text with the ruby position given by text-emphasis-position and the ruby alignment as centered. Note that this position may be adjusted if it would conflict with underline or overline decorations.

The effect of emphasis marks on the line height is the same as for ruby text.

Note, the preferred position of emphasis marks depends on the language. In Japanese for example, the preferred position is over right. In Chinese, on the other hand, the preferred position is under right. The informative table below summarizes the preferred emphasis mark positions for Chinese and Japanese:
Preferred emphasis mark and ruby position
Language Preferred position Illustration
Horizontal Vertical
Japanese over right Emphasis marks appear over each emphasized character in horizontal Japanese text. Emphasis marks appear on the right of each emphasized character in vertical Japanese text.
Korean
Mongolian
Chinese under right Emphasis marks appear below each emphasized character in horizontal Simplified Chinese text.

If emphasis marks are applied to characters for which ruby is drawn in the same position as the emphasis mark, the emphasis marks are placed outside the ruby. This includes auto-hidden and empty ruby annotations.

In this example, emphasis marks are applied to 4 characters, two of which have ruby.
		       The dots are placed above each character (aligned with the ruby) for the bare characters,
		       and above the ruby text for the annotated characters.

Emphasis marks applied to 4 characters, with ruby also on 2 of them

Some editors prefer to hide emphasis marks when they conflict with ruby. In HTML, this can be done with the following style rule:
ruby { text-emphasis: none; }

Some other editors prefer to hide ruby when they conflict with emphasis marks. In HTML, this can be done with the following pattern:

em { text-emphasis: dot; } /* Set text-emphasis for <em> elements */
em rt { display: none; }   /* Hide ruby inside <em> elements */

3.5. Emphasis Mark Skip: the text-emphasis-skip property

This section is under brainstorming. It’s also not yet clear if this property is needed quite yet, despite differences in desired behavior among publications.

Name: text-emphasis-skip
Value: spaces || punctuation || symbols || narrow
Initial: spaces punctuation
Applies to: text
Inherited: yes
Percentages: N/A
Computed value: specified keyword(s)
Canonical order: per grammar
Animation type: discrete

This property describes for which characters marks are drawn. The values have following meanings:

spaces
Skip word separators or other characters belonging to the Unicode separator category (Z*). (But note that emphasis marks are drawn for a space that combines with any combining characters.)
punctuation
Skip punctuation. Punctuation in this definition includes characters belonging to the Unicode P* category that are not defined as symbols (see below).
symbols
Skip symbols. Symbols in this definition includes all typographic character units belonging to the Unicode S* general category as well as any which are NFKD-equivalent [UAX15] to the following characters from the Unicode Po category:
# U+0023 NUMBER SIGN
% U+0025 PERCENT SIGN
U+2030 PER MILLE SIGN
U+2031 PER TEN THOUSAND SIGN
٪ U+066A ARABIC PERCENT SIGN
؉ U+0609 ARABIC-INDIC PER MILLE SIGN
؊ U+060A ARABIC-INDIC PER TEN THOUSAND SIGN
& U+0026 AMPERSAND
U+204A TIRONIAN SIGN E[[
@ U+0040 COMMERCIAL AT
§ U+00A7 SECTION SIGN
U+00B6 PILCROW SIGN
U+204B REVERSED PILCROW SIGN
U+2053 SWUNG DASH
〽️ U+303D PART ALTERNATION MARK
narrow
Skip characters where the East_Asian_Width property [UAX11] of the Unicode database [UAX44] is not F (Fullwidth) or W (Wide).

Characters belonging to the Unicode classes for control codes and unassigned characters (Cc, Cf, Cn) are skipped regardless of the value of this property.

This syntax requires UA to implement drawing marks for spaces. Is there any use case for doing so? If not, should we modify the syntax not to allow drawing marks for spaces?

See also discussion of the initial value.

4. Text Shadows: the text-shadow property

Name: text-shadow
Value: none | <shadow>#
Initial: none
Applies to: text
Inherited: yes
Percentages: n/a
Computed value: either the keyword none or a list, each item consisting of four absolute lengths plus a computed color and optionally also an inset keyword
Canonical order: per grammar
Animation type: as shadow list

This property accepts a comma-separated list of shadow effects to be applied to the text of the element. Values are interpreted as for box-shadow [CSS-BACKGROUNDS-3]. Each layer shadows the element’s text and all its text decorations (composited together). The shadow effects are applied front-to-back: the first shadow is on top. The shadows may thus overlay each other.

Unlike box-shadow, the spread distance is strictly interpreted as outset distance from any point of the glyph outline, and therefore, similar to the blur radius, creates rounded, rather than sharp, corners. Negative spread values are invalid.

Leave corner shaping undefined? [Issue #7250]

Outer text shadows (specified without the inset keyword) shadow the text—including any text stroke [FILL-STROKE-3]as if it were cut and raised above the surrounding canvas. Unlike box-shadow, outer text shadows are not clipped to the shadowed shape and may show through if the text is partially-transparent.

Inner text shadows (specified with the inset keyword) shadow the canvas—and any text stroke [FILL-STROKE-3]as if the text were cut and dropped below the surrounding canvas. They are therefore only drawn within the inner edge of the stroke.

Outer text shadows must be painted at a stack level between the element’s border/background (if present) and the elements text and text decoration. Inner text shadows must be painted over the text and its decorations. UAs should avoid painting text shadows over text in adjacent elements belonging to the same stack level and stacking context. (This may mean that the exact stack level of the shadows depends on whether the element has a border or background: the exact stacking behavior of text shadows is thus UA-defined.)

Stacking relationship to stroke? [Issue #7251]

Like box-shadow, text shadows do not influence layout, and do not trigger scrolling or increase the size of the scrollable overflow region.

The text-shadow property applies to both the ::first-line and ::first-letter pseudo-elements.

5. Painting Text Decorations

5.1. Painting Order of Text Decorations

As in [CSS2], text decorations are drawn immediately over/under the text they decorate, in the following order (bottommost first):

Where line decorations are drawn across box decorations or atomic inlines, they are drawn over non-positioned content and just below any positioned descendants (immediately below layer #8 in CSS2.1 Appendix E).

5.2. Overflow of Text Decorations

Text decorations that leak outside a box are considered ink overflow: they do not extend the scrollable overflow region. [css-overflow-3]

Appendix A: Acknowledgements

This specification would not have been possible without the help from: Ayman Aldahleh, Bert Bos, Tantek Çelik, Stephen Deach, John Daggett, Martin Dürst, Laurie Anna Edlund, Ben Errez, Yaniv Feinberg, Arye Gittelman, Ian Hickson, Martin Heijdra, Richard Ishida, Masayasu Ishikawa, Michael Jochimsen, Eric LeVine, Ambrose Li, Håkon Wium Lie, Chris Lilley, Ken Lunde, Nat McCully, Shinyu Murakami, Paul Nelson, Chris Pratley, Marcin Sawicki, Arnold Schrijver, Rahul Sonnad, Michel Suignard, Takao Suzuki, Frank Tang, Chris Thrasher, Etan Wexler, Chris Wilson, Masafumi Yabe and Steve Zilles.

Appendix B: Default UA Stylesheet

This appendix is informative, and is to help UA developers to implement default stylesheet, but UA developers are free to ignore or change.

/* typical styling of HTML */
blink {
  text-decoration-line: blink;
}
s, strike, del {
  text-decoration: line-through;
}
u, ins, :link, :visited {
  text-decoration: underline;
}
abbr[title], acronym[title] {
  text-decoration: dotted underline;
}

/* disable inheritance of text-emphasis marks to ruby text:
  emphasis marks should only apply to base text */
rt { text-emphasis: none; }

/* set language-appropriate default emphasis mark position */
:root:lang(zh), [lang|=zh] { text-emphasis-position: under right; }
[lang|=ja], [lang|=ko]     { text-emphasis-position: over right; }

/* set language-appropriate default underline position */
:root:lang(ja), [lang|=ja],
:root:lang(mn), [lang|=mn],
:root:lang(ko), [lang|=ko] { text-underline-position: right; }
:root:lang(zh), [lang|=zh] { text-underline-position: left;  }
/* auto is chosen (implied) above instead of under
   due to content-compatibility concerns */

If you find any issues, recommendations to add, or corrections, please send the information to www-style@w3.org with [css-text-decor] in the subject line.

While text-decoration-line: blink can’t be fully reproduced with other existing properties, authors can achieve a very similar effect with the following CSS:
@keyframes blink {
  0% {
    visibility: hidden;
    animation-timing-function: step-end;
  }
  25%, 100% {
    visibility: visible;
  }
}
blink {
  animation: blink 1s infinite;
}

Appendix C: Changes

Changes since the 6 May 2020 Working Draft

Significant changes since the 6 May 2020 Working Draft:

Additions Since Level 3

The following features have been added since Level 3:

6. Privacy and Security Considerations

This specification introduces no new privacy or security considerations.

Conformance

Document conventions

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:

This is an example of an informative example.

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.

Tests

Tests relating to the content of this specification may be documented in “Tests” blocks like this one. Any such block is non-normative.


Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

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.

Partial implementations

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.

Implementations of Unstable and Proprietary Features

To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

Non-experimental implementations

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.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

[CSS-BACKGROUNDS-3]
Bert Bos; Elika Etemad; Brad Kemper. CSS Backgrounds and Borders Module Level 3. 26 July 2021. CR. URL: https://www.w3.org/TR/css-backgrounds-3/
[CSS-BREAK-4]
Rossen Atanassov; Elika Etemad. CSS Fragmentation Module Level 4. 18 December 2018. WD. URL: https://www.w3.org/TR/css-break-4/
[CSS-CASCADE-5]
Elika Etemad; Miriam Suzanne; Tab Atkins Jr.. CSS Cascading and Inheritance Level 5. 13 January 2022. CR. URL: https://www.w3.org/TR/css-cascade-5/
[CSS-COLOR-4]
Tab Atkins Jr.; Chris Lilley; Lea Verou. CSS Color Module Level 4. 15 December 2021. WD. URL: https://www.w3.org/TR/css-color-4/
[CSS-DISPLAY-3]
Tab Atkins Jr.; Elika Etemad. CSS Display Module Level 3. 3 September 2021. CR. URL: https://www.w3.org/TR/css-display-3/
[CSS-FONTS-3]
John Daggett; Myles Maxfield; Chris Lilley. CSS Fonts Module Level 3. 20 September 2018. REC. URL: https://www.w3.org/TR/css-fonts-3/
[CSS-FONTS-4]
John Daggett; Myles Maxfield; Chris Lilley. CSS Fonts Module Level 4. 21 December 2021. WD. URL: https://www.w3.org/TR/css-fonts-4/
[CSS-INLINE-3]
Dave Cramer; Elika Etemad; Steve Zilles. CSS Inline Layout Module Level 3. 27 August 2020. WD. URL: https://www.w3.org/TR/css-inline-3/
[CSS-OVERFLOW-3]
David Baron; Elika Etemad; Florian Rivoal. CSS Overflow Module Level 3. 23 December 2021. WD. URL: https://www.w3.org/TR/css-overflow-3/
[CSS-POSITION-3]
Elika Etemad; Tab Atkins Jr.. CSS Positioned Layout Module Level 3. 16 December 2021. WD. URL: https://www.w3.org/TR/css-position-3/
[CSS-PSEUDO-4]
Daniel Glazman; Elika Etemad; Alan Stearns. CSS Pseudo-Elements Module Level 4. 31 December 2020. WD. URL: https://www.w3.org/TR/css-pseudo-4/
[CSS-RUBY-1]
Elika Etemad; et al. CSS Ruby Annotation Layout Module Level 1. 2 December 2021. WD. URL: https://www.w3.org/TR/css-ruby-1/
[CSS-SYNTAX-3]
Tab Atkins Jr.; Simon Sapin. CSS Syntax Module Level 3. 24 December 2021. CR. URL: https://www.w3.org/TR/css-syntax-3/
[CSS-TEXT-3]
Elika Etemad; Koji Ishii; Florian Rivoal. CSS Text Module Level 3. 22 April 2021. CR. URL: https://www.w3.org/TR/css-text-3/
[CSS-TEXT-4]
Elika Etemad; et al. CSS Text Module Level 4. 18 March 2022. WD. URL: https://www.w3.org/TR/css-text-4/
[CSS-VALUES-3]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 3. 6 June 2019. CR. URL: https://www.w3.org/TR/css-values-3/
[CSS-VALUES-4]
Tab Atkins Jr.; Elika Etemad. CSS Values and Units Module Level 4. 16 December 2021. WD. URL: https://www.w3.org/TR/css-values-4/
[CSS-WRITING-MODES-4]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 4. 30 July 2019. CR. URL: https://www.w3.org/TR/css-writing-modes-4/
[CSS2]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. REC. URL: https://www.w3.org/TR/CSS21/
[FILL-STROKE-3]
Elika Etemad; Tab Atkins Jr.. CSS Fill and Stroke Module Level 3. 13 April 2017. WD. URL: https://www.w3.org/TR/fill-stroke-3/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://datatracker.ietf.org/doc/html/rfc2119
[SELECTORS-4]
Elika Etemad; Tab Atkins Jr.. Selectors Level 4. 21 November 2018. WD. URL: https://www.w3.org/TR/selectors-4/
[UAX11]
Ken Lunde 小林劍󠄁. East Asian Width. 23 August 2021. Unicode Standard Annex #11. URL: https://www.unicode.org/reports/tr11/tr11-39.html
[UAX15]
Ken Whistler. Unicode Normalization Forms. 27 August 2021. Unicode Standard Annex #15. URL: https://www.unicode.org/reports/tr15/tr15-51.html
[UAX24]
Ken Whistler. Unicode Script Property. 27 August 2021. Unicode Standard Annex #24. URL: https://www.unicode.org/reports/tr24/tr24-32.html
[UAX44]
Ken Whistler; Laurențiu Iancu. Unicode Character Database. 30 August 2021. Unicode Standard Annex #44. URL: https://www.unicode.org/reports/tr44/tr44-28.html

Informative References

[CSS-CASCADE-6]
Elika Etemad; Miriam Suzanne; Tab Atkins Jr.. CSS Cascading and Inheritance Level 6. 21 December 2021. WD. URL: https://www.w3.org/TR/css-cascade-6/
[CSS-TEXT-DECOR-3]
Elika Etemad; Koji Ishii. CSS Text Decoration Module Level 3. 13 August 2019. CR. URL: https://www.w3.org/TR/css-text-decor-3/
[CSS3-ANIMATIONS]
Dean Jackson; et al. CSS Animations Level 1. 11 October 2018. WD. URL: https://www.w3.org/TR/css-animations-1/

Property Index

Name Value Initial Applies to Inh. %ages Anim­ation type Canonical order Com­puted value
text-decoration <'text-decoration-line'> || <'text-decoration-thickness'> || <'text-decoration-style'> || <'text-decoration-color'> see individual properties see individual properties see individual properties see individual properties see individual properties per grammar see individual properties
text-decoration-color <color> currentcolor all elements no n/a by computed value type per grammar computed color
text-decoration-line none | [ underline || overline || line-through || blink ] | spelling-error | grammar-error none all elements no (but see prose, above) n/a discrete per grammar specified keyword(s)
text-decoration-skip none | auto See individual properties all elements yes N/A discrete per grammar See individual properties
text-decoration-skip-box none | all none all elements yes N/A discrete per grammar specified keyword(s)
text-decoration-skip-ink auto | none | all auto all elements yes N/A discrete per grammar specified keyword
text-decoration-skip-inset none | auto none all elements yes N/A discrete per grammar specified keyword(s)
text-decoration-skip-self none | objects objects all elements yes N/A discrete per grammar specified keyword(s)
text-decoration-skip-spaces none | all | [ start || end ] start end all elements yes N/A discrete per grammar specified keyword(s)
text-decoration-style solid | double | dotted | dashed | wavy solid all elements no n/a discrete per grammar specified keyword
text-decoration-thickness auto | from-font | <length> | <percentage> auto all elements no N/A by computed value per grammar specified keyword or absolute length
text-emphasis <'text-emphasis-style'> || <'text-emphasis-color'> see individual properties see individual properties see individual properties see individual properties see individual properties per grammar see individual properties
text-emphasis-color <color> currentcolor text yes n/a by computed value type per grammar computed color
text-emphasis-position [ over | under ] && [ right | left ]? over right text yes n/a discrete per grammar specified keyword(s)
text-emphasis-skip spaces || punctuation || symbols || narrow spaces punctuation text yes N/A discrete per grammar specified keyword(s)
text-emphasis-style none | [ [ filled | open ] || [ dot | circle | double-circle | triangle | sesame ] ] | <string> none text yes n/a discrete per grammar the keyword none, a pair of keywords representing the shape and fill, or a string
text-shadow none | <shadow># none text yes n/a as shadow list per grammar either the keyword none or a list, each item consisting of four absolute lengths plus a computed color and optionally also an inset keyword
text-underline-offset auto | <length> | <percentage> auto all elements yes N/A by computed value per grammar specified keyword or absolute length
text-underline-position auto | [ from-font | under ] || [ left | right ] auto all elements yes n/a discrete per grammar specified keyword(s)

Issues Index

This section is copied over from early drafts of Text Decoration Level 3. It is still under review, and needs integration with text-underline-offset and text-decoration-thickness.
For simplicity, line-throughs should draw over each element at that element’s preferred/averaged position. This can produce some undesirable jumpiness, but there doesn’t appear to be any way to avoid that which is correct in all instances, and all attempts are worryingly complex. What position should line-throughs adopt over elements that have a different font-size, but no considered text?
The CSSWG resolved to be split skipping functionality into individual properties along the lines of text-decoration-skip-ink, to improve its cascading behavior. See discussion and resolution. This section is a rough draft and has not yet been vetted by the CSSWG
Is this none definition Web-compatible? Do we also need to add an ink value for Web-compat?
The CSSWG resolved to split text-decoration-skip into sub-properties, but this value set has not yet been vetted by the CSSWG.
The CSSWG resolved to split text-decoration-skip into sub-properties, but this value set has not yet been vetted by the CSSWG.
The CSSWG resolved to split text-decoration-skip into sub-properties, but this value set has not yet been vetted by the CSSWG.
This might want to be a standalone property rather than part of the text-decoration-skip set. See also Issue 4557, about controlling the line length explicitly.
Should the initial value be none for Web-compat? If not, INS and DEL at least should be assigned none in the UA default stylesheet. See also Issue 4653.
Ideographic scripts do not want to skip when auto. How can we define this behavior? Are there more scripts wanting not to skip? Need some normative text describe how auto works. See telcon minutes, alreq#86, csswg#1288
Are there other (non-CJK) scripts where it would be preferable to disable ink-skipping by default (when auto is in effect)? Perhaps Yi? Arabic? (See also discussion in Issue 1288.)
See also issue about continuity in size/position.
This section is under brainstorming. It’s also not yet clear if this property is needed quite yet, despite differences in desired behavior among publications.
This syntax requires UA to implement drawing marks for spaces. Is there any use case for doing so? If not, should we modify the syntax not to allow drawing marks for spaces?
See also discussion of the initial value.
Leave corner shaping undefined? [Issue #7250]
Stacking relationship to stroke? [Issue #7251]
If you find any issues, recommendations to add, or corrections, please send the information to www-style@w3.org with [css-text-decor] in the subject line.