[css-fonts-4] port font-variant-alternates from Fonts 3

Author: svgeesus

css-fonts-4/Overview.bs

@@ -2835,6 +2835,60 @@ p { font-variant-alternates: swash(unknown-value); } /* not a defined value, ign
 p { font-variant-alternates: normal; }
 </pre>
 
+This allows values to be defined and used for a given set of font
+families but ignored if fallback occurs, since the font family name
+would be different. If a given value is outside the range supported by
+a given font, the value is ignored.  These values never apply to
+generic font families.
+
+Individual values have the following meanings:
+
+<dl dfn-for="font-variant-alternates" dfn-type="value">
+	<dt><dfn id="font-variant-alternates-normal-value" title="normal!!font-variant-alternates">normal</dfn>
+	<dd>None of the features listed below are enabled.</dd>
+
+	<dt><dfn>historical-forms</dfn>
+	<dd>Enables display of historical forms (OpenType feature: <span class="tag">hist</span>).</dd>
+
+	<div class="featex"><img alt="historical form example" src="images/hist.png"></div>
+
+	<dt><dfn id="stylistic" title="stylistic">stylistic(&lt;feature-value-name&gt;)</dfn>
+	<dd>Enables display of stylistic alternates (<em>font specific</em>, OpenType feature: <span class="tag">salt &lt;feature-index&gt;</span>).</dd>
+
+	<div class="featex"><img alt="stylistic alternate example" src="images/salt.png"></div>
+
+	<dt><dfn id="styleset" title="styleset">styleset(&lt;feature-value-name&gt; #)</dfn>
+	<dd>Enables display with stylistic sets (<em>font specific</em>, OpenType feature: <span class="tag">ss&lt;feature-index&gt;</span>
+		OpenType currently defines <span class="tag">ss01</span> through <span class="tag">ss20</span>).</dd>
+
+	<div class="featex"><img alt="styleset example" src="images/ssnn.png"></div>
+
+	<dt><dfn id="character-variant" title="character-variant">character-variant(&lt;feature-value-name&gt; #)</dfn>
+	<dd>Enables display of specific character variants (<em>font specific</em>, OpenType feature: <span class="tag">cv&lt;feature-index&gt;</span>
+		OpenType currently defines <span class="tag">cv01</span> through <span class="tag">cv99</span>).</dd>
+
+	<dt><dfn id="swash" title="swash">swash(&lt;feature-value-name&gt;)</dfn>
+	<dd>Enables display of swash glyphs (<em>font specific</em>, OpenType feature: <span class="tag">swsh &lt;feature-index&gt;, cswh &lt;feature-index&gt;</span>).</dd>
+
+	<div class="featex"><img alt="swash example" src="images/swsh.png"></div>
+
+	<dt><dfn id="ornaments" title="ornaments">ornaments(&lt;feature-value-name&gt;)</dfn>
+	<dd>Enables replacement of default glyphs with ornaments, if provided in the font (<em>font specific</em>, OpenType feature: <span class="tag">ornm &lt;feature-index&gt;</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
+	alternates for the bullet character (U+2022) to allow authors to select the desired glyph using 'ornaments'.
+	</dd>
+
+	<div class="featex"><img alt="ornaments example" src="images/ornm.png"></div>
+
+	<dt><dfn id="annotation" title="annotation">annotation(&lt;feature-value-name&gt;)</dfn>
+	<dd>Enables display of alternate annotation forms (<em>font specific</em>, OpenType feature: <span class="tag">nalt &lt;feature-index&gt;</span>).</dd>
+
+	<div class="featex"><img alt="alternate annotation form example" src="images/nalt.png"></div>
+
+  </dl>
+
 Issue: Moved to Level 4; port the text for this from Fonts 3 .src to Fonts 4 .bs
 
 <h3 id="font-feature-values">