[css-fonts-4] Add the font-named-instance descriptor

w3c#525

Author: litherum

css-fonts-4/Overview.bs

@@ -211,29 +211,8 @@ Relationship Between Faces and Families
     font families with a variety of weights, widths, and slopes
     (see [[#platform-props-to-css]] for more details).
 
-    Some font file formats allow
-    font faces to carry multiple localizations
-    of the family name.
-    User agents must recognize and correctly match all of these names
-    independent of the underlying platform localization,
-    system API used, or document encoding.
-
-    <div class="example">
-        For example,
-        for each of the fonts listed below,
-        the author can use either the Latin name
-        or the localized name
-        in the 'font-family!!property' property,
-        and the results will be identical on all systems:
-        <figure>
-            <img alt="examples of localized family names" src="images/localizedfamilynames.png" >
-            <figcaption>Localized family names</figcaption>
-        </figure>
-    </div>
-
-    The details of localized font family name matching
-    and the corresponding issues of case sensitivity
-    are described below in [[#font-family-casing]].
+    See [[#localized-name-matching]] below for information on how
+    font-family names are matched.
 
 <h4 id="generic-font-families">
 Generic font families</h4>
@@ -2130,7 +2109,7 @@ by the underlying font.
 
 <h4 id="composite-fonts">Using character ranges to define composite fonts</h4>
 
-Multiple <code>@font-face</code> rules with different unicode ranges for the same
+Multiple ''@font-face'' rules with different unicode ranges for the same
 family and style descriptor values can be used to create composite fonts
 that mix the glyphs from different fonts for different scripts. This
 can be used to combine fonts that only contain glyphs for a single
@@ -2139,7 +2118,7 @@ way of segmenting a font into fonts for commonly used characters and
 less frequently used characters. Since the user agent will only pull
 down the fonts it needs this helps reduce page bandwidth.
 
-If the unicode ranges overlap for a set of <code>@font-face</code> rules with the
+If the unicode ranges overlap for a set of ''@font-face'' rules with the
 same family and style descriptor values, the rules are ordered in the
 reverse order they were defined; the last rule defined is the first to
 be checked for a given character.
@@ -2162,7 +2141,7 @@ Example ranges for specific languages or characters:
 
 <div class="example">
 	The BBC provides news services in a wide variety of languages, many
-	that are not well supported across all platforms. Using an <code>@font-face</code>
+	that are not well supported across all platforms. Using an ''@font-face''
 	rule, the BBC could provide a font for any of these languages, as it
 	already does via a manual font download.</p>
 <pre>
@@ -2266,7 +2245,7 @@ body { font-family: DroidSans; }
 	Next, the user agent evaluates the Japanese font. The unicode-range for
 	the Japanese font, U+3000-9FFF and U+ff??, does not include U+21E8, so
 	the user agent does not download the Japanese font.
-	Next the fallback font is considered. The <code>@font-face</code> rule for the
+	Next the fallback font is considered. The ''@font-face'' rule for the
 	fallback font does not define unicode-range so its value defaults to
 	the range of all Unicode code points. The fallback font is downloaded and
 	used to render the arrow character.
@@ -2308,28 +2287,80 @@ For: @font-face
 </pre>
 
 These descriptors define initial settings that apply when the font defined by
-an <code>@font-face</code> rule is rendered.  They do not affect font selection.
+an ''@font-face'' rule is rendered.  They do not affect font selection.
 Values are identical to those defined for the corresponding
 'font-variant!!property', 'font-feature-settings!!property', and
 'font-variation-settings!!property' properties defined below
-except that the <a>CSS-wide keywords</a> are omitted.  When multiple font
-feature descriptors, properties, or variations are used, the cumulative effect on
+except that the <a>CSS-wide keywords</a> are omitted. When multiple font
+feature descriptors, properties, or variations are used, optionally along with a named instance,
+the cumulative effect on
 text rendering is detailed in the section
-<a href="#font-feature-variation-resolution">Font Feature and Variation Resolution</a> below.
+[[#font-feature-variation-resolution]] below.
 In cases where specific values define synthesized fallback for certain
 'font-variant!!property' subproperties, the same synthesized fallback
 applies when used within those values are used with the
 'font-variant!!descriptor' descriptor.
 
+These descriptors set features and variation values
+on the font object which the ''@font-face'' rule represents,
+rather than on an entire element.
+Therefore, when using these descriptors,
+only some glyphs in an element may be rendered with that feature,
+due to [[#cluster-matching]].
+
+<h3 id="font-named-instance">Using named instances from variable fonts: the 'font-named-instance!!descriptor' descriptor</h3>
+
+<pre class='descdef'>
+Name: font-named-instance
+Value: auto | <string>
+Initial: auto
+For: @font-face
+</pre>
+
+If the 'font-named-instance!!descriptor' descriptor is set
+to a value other than 'font-named-instance/auto',
+then the appropriate stage in the [[#font-feature-variation-resolution]]
+will inspect the font file to find the first named instance in
+the font which has a localized name equal to the given <string>
+according to the rules given in [[#localized-name-matching]].
+If no such named instance exists,
+this descriptor is treated as if it has a value of 'font-named-instance/auto'.
+Otherwise, this named instance's variation axis values
+are applied a this position in the [[#font-feature-variation-resolution]].
+
+<div class="example">
+For example, the following ''@font-face'' block will
+apply the instance named "Grotesque"
+but will override the "XHGT" axis to have a value of 0.7.
+
+<pre>
+@font-face {
+    font-family: "AccuroVar";
+    src: url("accurovar.otf") format("opentype");
+    font-named-instance: "Grotesque";
+    font-variation-settings: "XHGT" 0.7;
+}
+</pre>
+</div>
+
+Note: Because the variation axis values supplied in the
+   'font-weight!!property', 'font-stretch!!property', and 'font-style!!property' properties
+   are applied before
+   the value in the 'font-named-instance!!descriptor' descriptor,
+   there is no need to change the value of those properties
+   when a named instance is desired.
+
+<h3 id="font-requests">Font request guidelines</h3>
+
 <h4 id="font-face-loading">Font loading guidelines</h4>
 
-The <code>@font-face</code> rule is designed to allow lazy loading
+The ''@font-face'' rule is designed to allow lazy loading
 of font resources that are only downloaded when used within a
-document.  A stylesheet can include <code>@font-face</code> rules for
+document. A stylesheet can include ''@font-face'' rules for
 a library of fonts of which only a select set are used; user agents
 must only download those fonts that are referred to within the style
-rules applicable to a given page.  User agents that download all fonts
-defined in <code>@font-face</code> rules without considering whether
+rules applicable to a given page. User agents that download all fonts
+defined in ''@font-face'' rules without considering whether
 those fonts are in fact used within a page are considered
 non-conformant. In cases where a font might be downloaded in character
 fallback cases, user agents may download a font if it's contained within
@@ -2353,13 +2384,10 @@ h2 {
 }
 </pre>
 
-In cases where textual content is loaded before downloadable fonts
-are available, user agents may render text as it would be rendered if
-downloadable font resources are not available or they may render text
-transparently with fallback fonts to avoid a flash of text using a
-fallback font.  In cases where the font download fails user agents must
-display text, simply leaving transparent text is considered
-non-conformant behavior.  Authors are advised to use fallback fonts in
+In cases where textual content is loaded before downloadable fonts are available,
+user agents must render text according to the 'font-display!!descriptor' descriptor of that ''@font-face'' block.
+In cases where the font download fails, user agents must
+display the text visibly. Authors are advised to use fallback fonts in
 their font lists that closely match the metrics of the
 downloadable fonts to avoid large page reflows where possible.
 
@@ -2597,7 +2625,7 @@ For: @font-face
 Initial: normal
 </pre>
 
-This descriptor defines initial settings that apply when the font defined by an @font-face rule is rendered. It does not affect font selection. Values are identical to those defined for the 'font-language-override!!property' property defined below except that the value inherit is omitted. When multiple font feature descriptors, properties, or variations are used, the cumulative effect on text rendering is detailed in the section Font Feature and Variation Resolution below.
+This descriptor defines initial settings that apply when the font defined by an @font-face rule is rendered. It does not affect font selection. Values are identical to those defined for the 'font-language-override!!property' property defined below except that the value inherit is omitted. When multiple font feature descriptors, properties, or variations are used, the cumulative effect on text rendering is detailed in the section [[#font-feature-variation-resolution]] below.
 
 <h2 id="font-matching-algorithm">Font Matching Algorithm</h2>
 
@@ -2607,12 +2635,29 @@ a font family is chosen
 and a particular font face is selected
 containing a glyph for that character.
 
-<h3 id="font-family-casing">Case sensitivity of font family names</h3>
+<h3 id="localized-name-matching">Localized name matching</h3>
+
+    Some font file formats allow
+    font faces to carry multiple localizations
+    of a particular string
+    (e.g. family name or named instance).
+    User agents must recognize and correctly match all of these names
+    independent of the underlying platform localization,
+    system API used, or document encoding.
+
+    <div class="example">
+        For example,
+        for each of the fonts listed below,
+        the author can use either the Latin name
+        or the localized name
+        in the 'font-family!!property' property,
+        and the results will be identical on all systems:
+        <figure>
+            <img alt="examples of localized family names" src="images/localizedfamilynames.png" >
+            <figcaption>Localized family names</figcaption>
+        </figure>
+    </div>
 
-As part of the font matching algorithm outlined below,
-user agents must match font family names used in style rules
-with actual font family names contained in fonts available in a given environment
-or with font family names defined in ''@font-face'' rules.
 User agents must match these names case insensitively,
 using the "Default Caseless Matching" algorithm outlined in the Unicode specification [[!UNICODE]].
 This algorithm is detailed in section 3.13 entitled "Default Case Algorithms".
@@ -2685,11 +2730,9 @@ if all font style properties were set to their initial value.
 	3. For other family names, the user agent attempts to find the
 		family name among fonts defined via ''@font-face'' rules and then
 		among available installed fonts, matching names with a
-		<a href="#font-family-casing">case-insensitive comparison</a> as outlined
+		[[#localized-name-matching]] as outlined
 		in the section above.
-		On systems containing fonts with multiple localized font family
-		names, user agents must match any of these names independent of the
-		underlying system locale or platform API used.  If the font
+		If the font
 		resources defined for a given face in an ''@font-face'' rule are either
 		not available or contain invalid font data, then the face should be
 		treated as not present in the family. If no faces are present for a
@@ -2709,8 +2752,7 @@ if all font style properties were set to their initial value.
 		before any layout or rendering occurs. The application of these values
 		must be applied in the <a href="#apply-font-matching-variations">Apply
 		font matching variations</a> step detailed in
-		<a href="#font-feature-variation-resolution">Font Feature and Variation
-		Resolution</a>.
+		[[#font-feature-variation-resolution]].
 		A group
 		of faces defined via ''@font-face'' rules with identical font
 		descriptor values but differing 'unicode-range' values are considered to be
@@ -3860,16 +3902,16 @@ resolved in the order below, in ascending order of precedence.  This ordering is
 used to construct a combined list of font features that affect a given
 text run.
 
-1. Font features enabled by default, including features required for a given script.
+1. Font features enabled by default are applied, including features required for a given script.
 
 2. <span id="apply-font-matching-variations">Font variations as enabled by the 'font-weight!!property',
-		'font-stretch!!property', and 'font-style!!property' properties.</span>
+		'font-stretch!!property', and 'font-style!!property' properties are applied.</span>
 
 	The application of the value enabled by
 	'font-style!!property' is affected by font selection, because this property might select an
 	italic or an oblique font. The value applied is the closest matching value as determined
 	by the <a href="#font-style-matching">font matching algorithm</a>. User Agents must apply
-	at most one value due to the 'font-style!!property' property; both "ital" and "slnt" values should
+	at most one value due to the 'font-style!!property' property; both "ital" and "slnt" values must
 	not be set together.
 
 	If the selected font is defined in an ''@font-face'' rule, then the values applied at this step
@@ -3880,40 +3922,48 @@ text run.
 	Then, the values applied in this step should be clamped (possibly again) to the values
 	that are supported by the font.
 
-3. The language specified by the inherited value of lang/xml:lang
+3. The language specified by the inherited value of lang/xml:lang is applied.
 
 4. If the font is defined via an ''@font-face'' rule, the font language override
-	implied by the 'font-language-override!!descriptor' descriptor in the ''@font-face'' rule.
+	implied by the 'font-language-override!!descriptor' descriptor in the ''@font-face'' rule are applied.
+
+5. If the font is defined via an ''@font-face'' rule, that ''@font-face'' rule includes
+    at least one valid 'font-named-instance' descriptor
+    with a value other than 'font-named-instance/none',
+    and the loaded font resource includes a named instance with that name
+    according to the [[#localized-name-matching]] rules,
+    then all the variation values represented by that named instance are applied.
+    These values are clamped to the values that are supported by the font.
 
-5. If the font is defined via an ''@font-face'' rule, the font variations
-	implied by the 'font-variation-settings!!descriptor' descriptor in the ''@font-face'' rule.
+6. If the font is defined via an ''@font-face'' rule, the font variations
+	implied by the 'font-variation-settings!!descriptor' descriptor in the ''@font-face'' rule are applied.
 
-6. If the font is defined via an ''@font-face'' rule, the font features
-	implied by the 'font-feature-settings!!descriptor' descriptor in the ''@font-face'' rule.
+7. If the font is defined via an ''@font-face'' rule, the font features
+	implied by the 'font-feature-settings!!descriptor' descriptor in the ''@font-face'' rule are applied.
 
-7. The font language override implied by the value of the 'font-language-override!!property' property.
+8. The font language override implied by the value of the 'font-language-override!!property' property is applied.
 
-8. Font variations implied by the value of the 'font-optical-sizing!!property' property.
+9. Font variations implied by the value of the 'font-optical-sizing!!property' property are applied.
 
-9. Font features implied by the value of the 'font-variant!!property' property,
+10. Font features implied by the value of the 'font-variant!!property' property,
 	the related 'font-variant!!property' subproperties and any other CSS property
-	that uses OpenType features (e.g. the 'font-kerning!!property' property).
+	that uses OpenType features (e.g. the 'font-kerning!!property' property) are applied.
 
 	<!-- other CSS props override 'font-variant' but not 'font-feature-settings' -->
 	<!-- http://lists.w3.org/Archives/Public/www-style/2013Aug/0110.html -->
 
-10. Feature settings determined by properties other than 'font-variant!!property' or
-	'font-feature-settings!!property'. For example, setting a
+11. Feature settings determined by properties other than 'font-variant!!property' or
+	'font-feature-settings!!property' are applied. For example, setting a
 	non-default value for the 'letter-spacing' property disables common ligatures.
 
-11. Font variations implied by the value of the 'font-variation-settings!!property' property.
+12. Font variations implied by the value of the 'font-variation-settings!!property' property are applied.
 	These values should be clamped to the values that are supported by the font.
 
-12. Font features implied by the value of 'font-feature-settings!!property' property.
+13. Font features implied by the value of 'font-feature-settings!!property' property are applied.
 
 This ordering allows authors to set up a general set of defaults
 for fonts within their ''@font-face'' rules, then override them with
-property settings for specific elements.  General property settings
+property settings for specific elements. General property settings
 override the settings in ''@font-face'' rules and low-level font feature
 settings override 'font-variant!!property' property settings.