[css-fonts-4] JS-free probing of Unicode support w3c#5578

Author: svgeesus

css-fonts-4/Overview.bs

@@ -6434,7 +6434,12 @@ In contrast to older technologies
 and sent this information in HTTP headers)
 such probing must be done one font at a time,
 providing the font family name
-and then checking via script whether the font was loaded.
+and then checking
+(either via script,
+or by using unicode-range to selectively download webfonts
+depending on whether the user has a font by a certain name
+that supports a certain character)
+whether the font was loaded.
 This takes time, and checking for more than a few hundred fonts
 introduces a noticeable delay in page rendering.
 
@@ -6612,7 +6617,8 @@ Changes
 <!-- new ones at the top -->
 
 <ul>
-	<!-- to Nov 3 2020 -->
+	<!-- to Nov 12 2020 -->
+	<li>Clarified that JS-free probing of Unicode support of fonts is possible</li>
 	<li>Clarified OpenType feature tags are 4 characters, trailing-space padded</li>
 	<li>Added font metric override descriptors</li>
 	<li>Added link to font features enabled by default</li>