[css-fonts-5] Add vertical metrics overrides. w3c#6152

Author: fantasai

css-fonts-5/Overview.bs

@@ -184,21 +184,21 @@ the 'ascent-override', 'descent-override', and 'line-gap-override' descriptors</
 
 	<pre class='descdef'>
 	Name: ascent-override
-	Value: normal | <<percentage [0,Infinity]>>
+	Value: [ normal | <<percentage [0,Infinity]>> ]{1,2}
 	For: @font-face
 	Initial: normal
 	</pre>
 
 	<pre class='descdef'>
 	Name: descent-override
-	Value: normal | <<percentage [0,Infinity]>>
+	Value: [ normal | <<percentage [0,Infinity]>> ]{1,2}
 	For: @font-face
 	Initial: normal
 	</pre>
 
 	<pre class='descdef'>
 	Name: line-gap-override
-	Value: normal | <<percentage [0,Infinity]>>
+	Value: [ normal | <<percentage [0,Infinity]>> ]{1,2}
 	For: @font-face
 	Initial: normal
 	</pre>
@@ -208,6 +208,9 @@ the 'ascent-override', 'descent-override', and 'line-gap-override' descriptors</
 	<a spec="CSS-INLINE-3">descent metric</a>, and
 	<a spec="CSS-INLINE-3">line gap metric</a>
 	of the font, respectively.
+	The first value provides the value for the x axis,
+	and the second value provides the value for the y axis
+	(defaulting to ''ascent-override/normal'' if omitted).
 
 	<dl dfn-for="ascent-override!!descriptor,descent-override!!descriptor,line-gap-override!!descriptor" dfn-type=value>
 		<dt><dfn>normal</dfn>
@@ -234,6 +237,10 @@ the 'ascent-override', 'descent-override', and 'line-gap-override' descriptors</
 	They can, however, affect the behavior of ''line-height: normal''
 	and more generally the baseline alignment of [=inline-level=] content.
 
+	Note: Since these metrics are only applicable in the [=block axis=],
+	the y-axis value will only be used
+	when [=typesetting upright=] in vertical [=typographic modes=].
+
 <div class="example">
 	The percentage is resolved against different font sizes for different elements.
 
@@ -290,28 +297,28 @@ the 'superscript-position-override', 'subscript-position-override','superscript-
 
 	<pre class='descdef'>
 	Name: superscript-position-override
-	Value: normal | from-font | <<percentage>>
+	Value: [ normal | from-font | <<percentage>> ]{1,2}
 	For: @font-face
 	Initial: normal
 	</pre>
 
 	<pre class='descdef'>
 	Name: subscript-position-override
-	Value: normal | from-font | <<percentage>>
+	Value: [ normal | from-font | <<percentage>> ]{1,2}
 	For: @font-face
 	Initial: normal
 	</pre>
 
 	<pre class='descdef'>
 	Name: superscript-size-override
-	Value: normal | from-font | <<percentage [0,Infinity]>>
+	Value: [ normal | from-font | <<percentage [0,Infinity]>> ]{1,2}
 	For: @font-face
 	Initial: normal
 	</pre>
 
 	<pre class='descdef'>
 	Name: subscript-size-override
-	Value: normal | from-font | <<percentage [0,Infinity]>>
+	Value: [ normal | from-font | <<percentage [0,Infinity]>> ]{1,2}
 	For: @font-face
 	Initial: normal
 	</pre>
@@ -321,6 +328,9 @@ the 'superscript-position-override', 'subscript-position-override','superscript-
 	specify the superscript offset, subscript offset, superscript size, and subscript size
 	metrics of the font, respectively,
 	which are used to synthesize glyphs when required by 'font-variant-position'.
+	The first value provides the value for the x axis,
+	and the second value provides the value for the y axis
+	(defaulting to the first value if omitted).
 
 	<dl dfn-for="superscript-position-override!!descriptor,subscript-position-override!!descriptor,superscript-size-override!!descriptor,subscript-size-override!!descriptor" dfn-type=value>
 		<dt><dfn>normal</dfn>
@@ -339,6 +349,10 @@ the 'superscript-position-override', 'subscript-position-override','superscript-
 			the given percentage multiplied by the used font size.
 	</dl>
 
+	Note: Since these metrics are only applicable in the [=block axis=],
+	the y-axis value will only be used
+	when [=typesetting upright=] in [=vertical typographic modes=].
+
 <h2 id="font-rend-props">
 Font Feature Properties</h2>