[css-fonts-4] Merge font-variant-ligatures from CSS Fonts 3 #1653

Author: svgeesus

css-fonts-4/Overview.bs

@@ -3532,6 +3532,111 @@ on text rendering speed.</p>
 <h3 id="font-variant-ligatures-prop">
 Ligatures: the 'font-variant-ligatures' property</h3>
 
+
+
+<pre class="propdef">
+Name: font-variant-ligatures
+
+Value: <span title="normal!!font-variant-ligatures">normal</span> | <span title="none!!font-variant-ligatures">none</span> | [ <var>&lt;common-lig-values&gt;</var> || <var>&lt;discretionary-lig-values&gt;</var> || <var>&lt;historical-lig-values&gt;</var> || <var>&lt;contextual-alt-values&gt;</var> ]
+Initial: normal
+Applies to: all elements
+Inherited: yes
+Percentages: n/a
+Computed value: as specified
+Animation type: discrete
+</pre>
+
+<p>Ligatures and contextual forms
+are ways of combining glyphs
+to produce more harmonized forms.</p>
+
+<pre class="prod"><dfn id="common-lig-values"><var>&lt;common-lig-values&gt;</var></dfn>        = [ <span>common-ligatures</span> | <span>no-common-ligatures</span> ]</pre>
+
+<pre class="prod"><dfn id="discretionary-lig-values"><var>&lt;discretionary-lig-values&gt;</var></dfn> = [ <span>discretionary-ligatures</span> | <span>no-discretionary-ligatures</span> ]</pre>
+
+<pre class="prod"><dfn id="historical-lig-values"><var>&lt;historical-lig-values&gt;</var></dfn>    = [ <span>historical-ligatures</span> | <span>no-historical-ligatures</span> ]</pre>
+
+<pre class="prod"><dfn id="contextual-alt-values"><var>&lt;contextual-alt-values&gt;</var></dfn>    = [ <span>contextual</span> | <span>no-contextual</span> ]</pre>
+
+<p>Individual values have the following meanings:</p>
+
+<dl>
+	<dt><dfn id="font-variant-ligatures-normal-value" title="normal!!font-variant-ligatures">normal</dfn></dt>
+<dd>A value of <span title="normal!!font-variant-ligatures">'normal'</span>
+specifies that common default features are enabled,
+<a href="#font-feature-resolution">as described in detail
+in the next section</a>.
+For OpenType fonts,
+common ligatures and contextual forms are on by default,
+discretionary and historical ligatures are not.</dd>
+
+	<dt><dfn id="font-variant-ligatures-none-value" title="none!!font-variant-ligatures">none</var></dt>
+<dd>Specifies that all types of ligatures and contextual forms
+covered by this property
+are explicitly disabled.
+In situations where ligatures are not considered necessary,
+this <em>may</em>
+improve the speed of text rendering.</dd>
+
+	<dt><dfn>common-ligatures</dfn>
+<dd>Enables display of common ligatures
+(OpenType features: <span class="tag">liga, clig</span>).
+For OpenType fonts,
+common ligatures are enabled by default.</dd>
+
+	<div class="featex"><img alt="common ligature example" src="liga.png"></div>
+
+	<dt><dfn>no-common-ligatures</dfn>
+<dd>Disables display of common ligatures
+(OpenType features: <span class="tag">liga, clig</span>).</dd>
+
+	<dt><dfn>discretionary-ligatures</dfn>
+<dd>Enables display of discretionary ligatures
+(OpenType feature: <span class="tag">dlig</span>).
+Which ligatures are discretionary or optional is decided by the type designer,
+so authors will need to refer to
+the documentation of a given font
+to understand which ligatures are considered discretionary.</dd>
+
+	<div class="featex"><img alt="discretionary ligature example" src="dlig.png"></div>
+
+	<dt><dfn>no-discretionary-ligatures</dfn>
+<dd>Disables display of discretionary ligatures
+(OpenType feature: <span class="tag">dlig</span>).</dd>
+
+	<dt><dfn>historical-ligatures</dfn>
+<dd>Enables display of historical ligatures
+(OpenType feature: <span class="tag">hlig</span>).</dd>
+
+	<div class="featex"><img alt="historical ligature example" src="hlig.png"></div>
+
+	<dt><dfn>no-historical-ligatures</dfn>
+<dd>Disables display of historical ligatures
+(OpenType feature: <span class="tag">hlig</span>).</dd>
+
+	<dt><dfn>contextual</dfn>
+<dd>Enables display of contextual alternates
+(OpenType feature: <span class="tag">calt</span>).
+Although not strictly a ligature feature,
+like ligatures this feature is commonly used
+to harmonize the shapes of glyphs with the surrounding context.
+For OpenType fonts,
+this feature is on by default.</dd>
+
+	<div class="featex"><img alt="contextual alternate example" src="calt.png"></div>
+
+	<dt><dfn>no-contextual</dfn>
+<dd>Disables display of contextual alternates
+(OpenType feature: <span class="tag">calt</span>).</dd>
+
+</dl>
+
+<p id=rlig-unaffected"><em>Required</em> ligatures,
+needed for correctly rendering complex scripts,
+are not affected by the settings above,
+including 'none'
+(OpenType feature: <span class="tag">rlig</span>).</p>
+
 <h3 id="font-variant-position-prop">
 Subscript and superscript forms: the 'font-variant-position' property</h3>