[css-fonts-4] Add math value to font-size, fix #5389

Author: svgeesus

css-fonts-4/Overview.bs

@@ -914,7 +914,7 @@ Font size: the 'font-size' property</h3>
 
     <pre class="propdef">
     Name: font-size
-    Value: <<absolute-size>> | <<relative-size>> | <<length-percentage>>
+    Value: <<absolute-size>> | <<relative-size>> | <<length-percentage>> | math
     Initial: medium
     Applies to: all elements and text
     Inherited: yes
@@ -989,6 +989,13 @@ Font size: the 'font-size' property</h3>
             Note: Use of percentage values or <a>font-relative lengths</a>
             such as ''em''s and ''rem''s
             leads to more robust and cascadable style sheets.
+		<dt><dfn>math</dfn></dt>
+		<dd>
+			Special <a href="https://w3c.github.io/mathml-core/#the-math-script-level-property">
+			mathematical scaling rules</a> must be applied
+			when determining the computed value of the 'font-size'
+			property.
+		</dd>
     </dl>
 
     <div class="example">
@@ -7330,6 +7337,7 @@ Changes
 
 <ul>
 	<!-- to 03 Dec 2021 -->
+	<li>New 'math' value added to 'font-size'</li>
 	<li>Security and Privacy are now separate sections</li>
 	<li>Linked to OpenType, TrueType and Graphite table definitions</li>
 	<li>Updated examples which had used "supports"</li>