[css-fonts-5] Start level 5 as CSSWG resolved to put stuff there today #126

Author: svgeesus

css-fonts-5/Overview.bs

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+<pre class='metadata'>
+Title: CSS Fonts Module Level 5
+Shortname: css-fonts
+Level: 5
+Status: ED
+Work Status: exploring
+Group: CSSWG
+ED: https://drafts.csswg.org/css-fonts-5/
+TR: https://www.w3.org/TR/css-fonts-5/
+!Delta Spec: yes
+Editor: Myles C. Maxfield, Apple Inc., mmaxfield@apple.com, w3cid 77180
+Editor: Chris Lilley, W3C, http://svgees.us, w3cid 1438
+Abstract: This specification defines modifications to the existing <a href="https://drafts.csswg.org/css-fonts-4/">CSS Fonts 4</a> specification along with additional features.
+Repository: w3c/csswg-drafts
+Inline Github Issues: title
+Default Highlight: css
+Warning: Not Ready
+</pre>
+
+<pre class="link-defaults">
+spec:css-color-4; type:property; text:color
+spec:css-values; type:value; text:ex
+spec:css22; type:value; for:/; text:block
+spec:html; type:element; text:font
+spec:css-fonts-4; type:descriptor; text:font-language-override
+</pre>
+
+
+<h2 id="introduction">
+Introduction</h2>
+
+The CSS Fonts Level 4 specification ([[!CSS-FONTS-4]]) describes the
+controls CSS provides for selecting and using fonts within documents,
+including support for variable fonts and color fonts.
+The ideas here are additions or modifications to the properties and
+rules defined in CSS Fonts Level 4.
+
+This specification is currently a delta to the CSS Fonts Level 4 specification.
+Do not assume that if something is not here, it has been dropped.
+
+
+
+<h3 id="values">
+Value Definitions</h3>
+
+This specification follows the <a href="https://www.w3.org/TR/CSS2/about.html#property-defs">CSS property definition conventions</a> from [[!CSS2]]
+using the <a href="https://www.w3.org/TR/css-values-3/#value-defs">value definition syntax</a> from [[!CSS-VALUES-3]].
+Value types not defined in this specification are defined in CSS Values &amp; 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 <a>CSS-wide keywords</a> as their property value.
+For readability they have not been repeated explicitly.
+
+<h2 id="basic-font-props">
+Basic Font Properties</h2>
+
+<h3 id="font-family-prop">
+    Font family: the 'font-family!!property' property</h3>
+
+<h4 id="generic-font-families">
+Generic font families</h4>
+
+In addition to the [[css-fonts-4#generic-font-families]]
+in CSS Fonts Level 4, the following new generic font families are also defined.
+
+Issue(4910):
+
+Issue(5054):
+
+    <dl dfn-for="font-family,<generic-family>" dfn-type=value>
+        <dt id="xxx-def"><dfn>xxx</dfn>
+        <dd>
+            Placeholder text for the xxx generic font family.
+
+
+    </dl>
+
+Issue(4566):
+
+<h3 id="font-weight-prop">Font weight: the 'font-weight!!property' property</h3>
+
+Issue(2690):
+
+
+<h3 id="font-style-prop">
+Font style: the 'font-style!!property' property</h3>
+
+Issue(4044):
+
+
+<h3 id="font-size-adjust-prop">
+Relative sizing: the 'font-size-adjust' property</h3>
+
+Issue(5539):
+
+
+<h2 id="font-resources">
+Font Resources</h2>
+
+<h3 id="font-face-rule">
+The <dfn id="at-font-face-rule">''@font-face''</dfn> rule</h3>
+
+Issue(5518):
+
+
+<h3 id="font-size-desc">
+Font property descriptors: the 'font-size!!descriptor'
+</h3>
+
+Issue(806):
+
+Issue(731):
+
+Issue(5892):
+
+
+<!-- should this stay in Fonts 4 or be here in Fonts 5? -->
+
+<h3 id="font-metrics-override-desc">
+Default font metrics overriding:
+the 'ascent-override', 'descent-override' and 'line-gap-override' descriptors</h3>
+
+<pre class='descdef'>
+Name: ascent-override
+Value: normal | <<percentage>>
+For: @font-face
+Initial: normal
+</pre>
+
+<pre class='descdef'>
+Name: descent-override
+Value: normal | <<percentage>>
+For: @font-face
+Initial: normal
+</pre>
+
+<pre class='descdef'>
+Name: line-gap-override
+Value: normal | <<percentage>>
+For: @font-face
+Initial: normal
+</pre>
+
+The 'ascent-override', 'descent-override' and 'line-gap-override' descriptors define the
+<a spec="CSS-INLINE-3">ascent metric</a>, <a spec="CSS-INLINE-3">descent metric</a> and
+<a spec="CSS-INLINE-3">line gap metric</a> of the font, respectively.
+
+When the descriptor value is 'normal', the corresponding metric value is obtained from the
+font file directly.
+
+Note: User agents may draw data from different places from the font file as the metric values,
+which results in different text layouts.
+
+When the descriptor value is a percentage, the corresponding metric value is resolved as the
+given percentage multiplied by the used font size. Negative values are invalid at parse time.
+
+<div class="example">
+	The percentage is resolved against different font sizes for different elements.
+
+<pre>
+@font-face {
+  font-family: overridden-font;
+  ascent-override: 50%;
+  ...
+}
+
+&lt;span style="font-family: overridden-font; font-size: 20px;"&gt;
+  Outer span content
+  &lt;span style="font-size: 150%;"&gt;Inner span content&lt;/span&gt;
+&lt;/span&gt;
+</pre>
+
+	The outer span uses an <a spec="CSS-INLINE-3" lt="ascent metric">ascent</a> value of
+	10px, whereas the inner span uses 15px.
+
+</div>
+
+<div class="example">
+	We may override the metrics of a local fallback font to match the primary font, which
+	is a web font. This reduces layout shifting when switching from fallback to the
+	primary font.
+
+<pre>
+@font-face {
+  font-family: cool-web-font;
+  src: url("https://example.com/font.woff");
+}
+
+@font-face {
+  font-family: fallback-to-local;
+  src: local(Some Local Font);
+  /* Override metric values to match cool-web-font */
+  ascent-override: 125%;
+  descent-override: 25%;
+  line-gap-override: 0%;
+}
+
+&lt;div style="font-family: cool-web-font, fallback-to-local"&gt;Title goes here&lt;/div&gt;
+&lt;img src="https://example.com/largeimage" alt="A large image that you don't want to shift"&gt;
+</pre>
+
+	The image will not be vertically shifted when the user agent finishes loading and
+	switches to use the web font.
+
+</div>
+
+<h3 id="font-sup-sub-override-desc">
+    Default font metrics overriding:
+    the 'superscript-position-override', 'subscript-position-override','superscript-size-override' and 'subscript-size-override' descriptors</h3>
+
+Issue(5518):
+
+    <pre class='descdef'>
+        Name: superscript-position-override
+        Value: normal | <<percentage>>
+        For: @font-face
+        Initial: normal
+    </pre>
+
+    <pre class='descdef'>
+        Name: subscript-position-override
+        Value: normal | <<percentage>>
+        For: @font-face
+        Initial: normal
+    </pre>
+
+    <pre class='descdef'>
+        Name: superscript-size-override
+        Value: normal | <<percentage>>
+        For: @font-face
+        Initial: normal
+    </pre>
+
+    <pre class='descdef'>
+        Name: subscript-size-override
+        Value: normal | <<percentage>>
+        For: @font-face
+        Initial: normal
+    </pre>
+
+
+
+<h2 id="font-rend-props">
+Font Feature Properties</h2>
+
+
+<h3 id="font-language-override-prop">Font language override: the 'font-language-override' property</h3>
+
+Issue(5484):
+
+
+<h2 id="font-feature-variation-resolution">
+Font Feature and Variation Resolution</h3>
+
+Issue(5635):
+
+
+<h2 id="font-variation-props">
+Font Variation Properties</h2>
+
+
+<h3 id="font-optical-sizing-def">
+Optical sizing control: the 'font-optical-sizing' property</h3>
+
+Issue(5466):
+
+
+<!-- This might get moved here -->
+<!--
+    <h2 id="color-font-support">
+Color Font Support</h2>
+-->
+
+
+<h2 id="priv-sec">
+Security and Privacy Considerations
+</h2>
+
+No new security or privacy considerations have been raised on this specification.
+
+
+<h2 id="acknowledgments">
+Acknowledgments</h2>
+
+The CSS Working group would like to thank:
+
+
+<h2 id="changes">
+Changes
+</h2>
+-->