[css-fonts-4] Add generic functional notation, fix #6770

css-fonts-4/Overview.bs

@@ -311,6 +311,26 @@ Syntax of <<family-name>>
 	with the keywords of the same names.
 	UAs must not consider these keywords as matching the <<family-name>> type.
 
+<h4 id="generic-family-name-syntax">
+Syntax of <<generic-family-name>>
+</h4>
+
+	<pre class=prod><l><<generic-family-name>></l> = generic( <<custom-ident>>+ ) | <<string>> | <<custom-ident>>+</pre>
+
+	<div class="example" id="ex-generic-functional">
+		More recently defined generic font families are identified using a functional syntax:
+
+		<pre>
+			body { font-family: "Adobe Fangsong Std R", generic(fangsong), serif}
+		</pre>
+
+		The first choice in this example is a specific font in fangsong style.
+		The family name is enclosed in quotes as it contains space characters.
+		The second is a recently added generic font; it is unicode-range specific
+		and so may not match to an actual installed font on some systems.
+		The third is a generic font, which is guaranteed to match on all systems.
+	</div>
+
 <h4 id="font-families">
 Relationship Between Faces and Families
 </h4>