[css-fonts-5] Add from-font value, computing to value from first available font. #5539

Author: fantasai

css-fonts-5/Overview.bs

@@ -95,7 +95,7 @@ Relative sizing: the 'font-size-adjust' property</h3>
 
 	<pre class="propdef">
 	Name: font-size-adjust
-	Value: none | <<number>>
+	Value: none | from-font | <<number>>
 	Initial: none
 	Applies to: all elements and text
 	Inherited: yes
@@ -213,6 +213,11 @@ Relative sizing: the 'font-size-adjust' property</h3>
 			text rendered using the first font in the family list
 			will display differently in older user agents
 			that don't support 'font-size-adjust'.
+
+		<dt><dfn>from-font</dfn>
+		<dd>
+			Computes to the <<number>> corresponding to
+			the <a>aspect value</a> of the [=first available font=].
 	</dl>
 
 	The value of 'font-size-adjust' affects the used value of 'font-size'