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[css-fonts-4] Clarify range constraints on descriptor values in <font-feature-value-type> #13324

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svgeesus merged 2 commits into from
Apr 17, 2026
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[css-fonts-4] Clarify range constraints on descriptor values in <font-feature-value-type> #13324

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d6323b3
[css-fonts-4] Rename <feature-*> to <font-feature-*>
cdoublev Jan 10, 2026
dd79487
[css-fonts-4] Clarify range constraints on descriptor values in <font…
cdoublev Jan 10, 2026
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64 changes: 37 additions & 27 deletions css-fonts-4/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -5808,13 +5808,13 @@ Alternates and swashes: the 'font-variant-alternates' property</h3>

<pre class="propdef">
Name: font-variant-alternates
Value: normal | [ stylistic(<<feature-value-name>>) ||
Value: normal | [ stylistic(<<font-feature-value-name>>) ||
historical-forms ||
styleset(<<feature-value-name>>#) ||
character-variant(<<feature-value-name>>#) ||
swash(<<feature-value-name>>) ||
ornaments(<<feature-value-name>>) ||
annotation(<<feature-value-name>>) ]
styleset(<<font-feature-value-name>>#) ||
character-variant(<<font-feature-value-name>>#) ||
swash(<<font-feature-value-name>>) ||
ornaments(<<font-feature-value-name>>) ||
annotation(<<font-feature-value-name>>) ]
Initial: normal
Applies to: all elements and text
Inherited: yes
Expand Down Expand Up @@ -5850,8 +5850,8 @@ Alternates and swashes: the 'font-variant-alternates' property</h3>
parsing/font-variant-alternates-valid.html
</wpt>

<pre class="prod"><dfn id="feature-index-value">&lt;feature-index&gt;</dfn> = <<integer [0,∞]>></pre>
<pre class="prod"><dfn id="feature-value-name-value">&lt;feature-value-name&gt;</dfn> = <<ident>></pre>
<pre class="prod"><dfn id="font-feature-index-value">&lt;font-feature-index&gt;</dfn> = <<integer>></pre>
<pre class="prod"><dfn id="font-feature-value-name-value">&lt;font-feature-value-name&gt;</dfn> = <<ident>></pre>

For any given character, fonts can provide a variety of alternate
glyphs in addition to the default glyph for that character. This
Expand All @@ -5865,8 +5865,8 @@ Alternates and swashes: the 'font-variant-alternates' property</h3>
of these alternates is font-specific, the
''@font-feature-values'' rule is used to define values for a
specific font family or set of families that associate a font-specific
numeric <<feature-index>> with a custom
<<feature-value-name>>, which is then used in this
numeric <<font-feature-index>> with a custom
<<font-feature-value-name>>, which is then used in this
property to select specific alternates:

<pre class=example id="ex-noble-script">
Expand All @@ -5878,10 +5878,10 @@ Alternates and swashes: the 'font-variant-alternates' property</h3>
}
</pre>

When a particular <<feature-value-name>> has not
When a particular <<font-feature-value-name>> has not
been defined for a given family or for a particular feature type, the
computed value must be the same as if it had been defined. However,
property values that contain these undefined <<feature-value-name>>
property values that contain these undefined <<font-feature-value-name>>
identifiers must be ignored when choosing glyphs.

<pre class=example id="ex-effectively-same">
Expand Down Expand Up @@ -5911,37 +5911,37 @@ Alternates and swashes: the 'font-variant-alternates' property</h3>
</div>
</dd>

<dt><dfn id="stylistic" title="stylistic">stylistic(<<feature-value-name>>)</dfn>
<dd>Enables display of stylistic alternates ([=font specific=], OpenType feature: <span class="tag">salt <<feature-index>></span>).
<dt><dfn id="stylistic" title="stylistic">stylistic(<<font-feature-value-name>>)</dfn>
<dd>Enables display of stylistic alternates ([=font specific=], OpenType feature: <span class="tag">salt <<font-feature-index>></span>).

<div class="featex">
<img alt="stylistic alternate example" src="images/salt.png" width="300" height="58">
</div>
</dd>

<dt><dfn id="styleset" title="styleset">styleset(<<feature-value-name>>#)</dfn>
<dd>Enables display with stylistic sets ([=font specific=], OpenType feature: <span class="tag">ss<<feature-index>></span>
<dt><dfn id="styleset" title="styleset">styleset(<<font-feature-value-name>>#)</dfn>
<dd>Enables display with stylistic sets ([=font specific=], OpenType feature: <span class="tag">ss<<font-feature-index>></span>
OpenType currently defines <span class="tag">ss01</span> through <span class="tag">ss20</span>).

<div class="featex">
<img alt="styleset example" src="images/ssnn.png" width="700" height="76">
</div>
</dd>

<dt><dfn id="character-variant" title="character-variant">character-variant(<<feature-value-name>>#)</dfn>
<dd>Enables display of specific character variants ([=font specific=], OpenType feature: <span class="tag">cv<<feature-index>></span>
<dt><dfn id="character-variant" title="character-variant">character-variant(<<font-feature-value-name>>#)</dfn>
<dd>Enables display of specific character variants ([=font specific=], OpenType feature: <span class="tag">cv<<font-feature-index>></span>
OpenType currently defines <span class="tag">cv01</span> through <span class="tag">cv99</span>).</dd>

<dt><dfn id="swash" title="swash">swash(<<feature-value-name>>)</dfn>
<dd>Enables display of swash glyphs ([=font specific=], OpenType feature: <span class="tag">swsh <<feature-index>>, cswh <<feature-index>></span>).
<dt><dfn id="swash" title="swash">swash(<<font-feature-value-name>>)</dfn>
<dd>Enables display of swash glyphs ([=font specific=], OpenType feature: <span class="tag">swsh <<font-feature-index>>, cswh <<font-feature-index>></span>).

<div class="featex">
<img alt="swash example" src="images/swsh.png" width="380" height="64">
</div>
</dd>

<dt><dfn id="ornaments" title="ornaments">ornaments(<<feature-value-name>>)</dfn>
<dd>Enables replacement of default glyphs with ornaments, if provided in the font ([=font specific=], OpenType feature: <span class="tag">ornm <<feature-index>></span>).
<dt><dfn id="ornaments" title="ornaments">ornaments(<<font-feature-value-name>>)</dfn>
<dd>Enables replacement of default glyphs with ornaments, if provided in the font ([=font specific=], OpenType feature: <span class="tag">ornm <<font-feature-index>></span>).
Some fonts may offer ornament glyphs as alternates for a wide collection of characters; however, displaying arbitrary
characters (e.g., alphanumerics) as ornaments is poor practice as it distorts the semantics of the data. Font designers
are encouraged to encode all ornaments (except those explicitly encoded in the Unicode Dingbats blocks, etc.) as
Expand All @@ -5952,8 +5952,8 @@ Alternates and swashes: the 'font-variant-alternates' property</h3>
</div>
</dd>

<dt><dfn id="annotation" title="annotation">annotation(<<feature-value-name>>)</dfn>
<dd>Enables display of alternate annotation forms ([=font specific=], OpenType feature: <span class="tag">nalt <<feature-index>></span>).
<dt><dfn id="annotation" title="annotation">annotation(<<font-feature-value-name>>)</dfn>
<dd>Enables display of alternate annotation forms ([=font specific=], OpenType feature: <span class="tag">nalt <<font-feature-index>></span>).

<div class="featex">
<img alt="alternate annotation form example" src="images/nalt.png" width="350" height="62">
Expand Down Expand Up @@ -6101,11 +6101,21 @@ Defining font specific alternates: the <dfn>@font-feature-values</dfn> rule</h3>
and the value must be a list of one or more non-negative <<integer>>s.

The [=feature value blocks=] accept any declaration name;
these names must be identifiers,
these names must be <<font-feature-value-name>>,
per standard CSS syntax rules,
and are [=case-sensitive=]
(so <css>foo: 1;</css> and <css>FOO: 2</css> define two different features).
Each declaration's value must match the grammar ''<<integer [0,∞]>>+'',

Each declaration's value in ''@annotation'', ''@ornaments'', ''@stylistic'', ''@swash'',
must match the grammar <<font-feature-index>>,
or else the declaration is invalid and must be ignored.

Each declaration’s value in ''@character-variant''
must match the grammar <<font-feature-index [0,99]>> <<font-feature-index [0,∞]>>,
or else the declaration is invalid and must be ignored.

Each declaration’s value in ''@styleset''
must match the grammar <<font-feature-index [0,20]>>+,
or else the declaration is invalid and must be ignored.

Note: Each feature name is unique only within a single [=feature value block=].
Expand Down Expand Up @@ -6514,7 +6524,7 @@ Overall shorthand for font rendering: the 'font-variant!!property' property</h3>

<pre class="propdef">
Name: font-variant
Value: normal | none | [ [ <<common-lig-values>> || <<discretionary-lig-values>> || <<historical-lig-values>> || <<contextual-alt-values>> ] || [ small-caps | all-small-caps | petite-caps | all-petite-caps | unicase | titling-caps ] || [ stylistic(<<feature-value-name>>) || historical-forms || styleset(<<feature-value-name>>#) || character-variant(<<feature-value-name>>#) || swash(<<feature-value-name>>) || ornaments(<<feature-value-name>>) || annotation(<<feature-value-name>>) ] || [ <<numeric-figure-values>> || <<numeric-spacing-values>> || <<numeric-fraction-values>> || ordinal || slashed-zero ] || [ <<east-asian-variant-values>> || <<east-asian-width-values>> || ruby ] || [ sub | super ] || [ text | emoji | unicode ] ]
Value: normal | none | [ [ <<common-lig-values>> || <<discretionary-lig-values>> || <<historical-lig-values>> || <<contextual-alt-values>> ] || [ small-caps | all-small-caps | petite-caps | all-petite-caps | unicase | titling-caps ] || [ stylistic(<<font-feature-value-name>>) || historical-forms || styleset(<<font-feature-value-name>>#) || character-variant(<<font-feature-value-name>>#) || swash(<<font-feature-value-name>>) || ornaments(<<font-feature-value-name>>) || annotation(<<font-feature-value-name>>) ] || [ <<numeric-figure-values>> || <<numeric-spacing-values>> || <<numeric-fraction-values>> || ordinal || slashed-zero ] || [ <<east-asian-variant-values>> || <<east-asian-width-values>> || ruby ] || [ sub | super ] || [ text | emoji | unicode ] ]
Initial: normal
Applies to: all elements and text
Inherited: yes
Expand Down