[css-fonts-4][css-values-4] Define 'font-affecting properties' and list which properties are in that category. #14306

Author: tabatkins

css-fonts-4/Overview.bs

@@ -99,6 +99,20 @@ Value Definitions</h3>
 	also accept the <a>CSS-wide keywords</a> as their property value.
 	For readability they have not been repeated explicitly.
 
+<h3 id="font-relative">
+Interaction With Font-Relative Units</h3>
+
+	The following properties defined in this specification are [=font-affecting properties=]:
+
+	* All longhands of the 'font' shorthand
+	* All longhands of the 'font-synthesis' shorthand
+	* All longhands of the 'font-variant' shorthand
+	* 'font-language-override'
+	* 'font-feature-settings'
+	* 'font-variation-settings'
+	* 'font-optical-sizing' 
+
+
 <h2 id="basic-font-props">
 Basic Font Properties</h2>
 

css-values-4/Overview.bs

@@ -2080,14 +2080,16 @@ Font-relative Lengths: the ''em'', ''rem'', ''ex'', ''rex'', ''cap'', ''rcap'',
 
 	</dl>
 
-	When used in the value of any 'font-*' property on the element they refer to,
+	Properties that affect the font size or font metrics of an element 
+	are <dfn export lt="font-affecting property">font-affecting properties</dfn>.
+	When used in the value of any [=font-affecting property=] on the element they refer to,
 	the [=font-relative lengths=] resolve against the computed metrics of the parent element--
 	or against the computed metrics corresponding to the initial values
 	of the 'font' and 'line-height' properties,
 	if the element has no parent.
 	Similarly,
 	when ''lh'' or ''rlh'' units are used
-	in the value of the 'line-height' property or 'font-*' properties on the element they refer to,
+	in the value of the 'line-height' property or [=font-affecting properties=] on the element they refer to,
 	they resolve against the computed 'line-height' and font metrics of the parent element--
 	or the computed metrics corresponding to the initial values
 	of the 'font' and 'line-height' properties,