[css-fonts-5] Mention examples related to text-decoration for size-adjust. w3c#5138

Author: fantasai

css-fonts-5/Overview.bs

@@ -160,10 +160,13 @@ the 'size-adjust' descriptor</h3>
 	are scaled by the given percentage,
 	as are the rendered glyph images.
 	Consequently,
-	any units derived from font metrics (such as ''ex'' and ''ch'')
+	any values derived from font metrics
+	(such as ''ex'' and ''ch'' units,
+	or the ''text-underline-thickness/from-font'' value of 'text-underline-thickness')
 	are also affected when sourced from this font.
 	However, the [=computed value|computed=] 'font-size'
-	(and thus any units such as ''em'' that derive from it)
+	(and thus any values that derive from it,
+	such as ''em'' units, percentages in 'text-underline-offset', etc.)
 	remains unaffected.
 
 	Note: The 'size-adjust' descriptor functions similarly to