[css-fonts-4] Describe classes of generics and whether they are guaranteed to match. #6770

Author: svgeesus

css-fonts-4/Overview.bs

@@ -216,17 +216,39 @@ Font family: the 'font-family!!property' property</h3>
 	    <dd>
 	        The name of a font family, such as Helvetica or Verdana in the previous example.
 
+			This might be a locally-instaled font, or might be a web font.
+
 	    <dt><dfn id="generic-family-value"><<generic-family>></dfn>
 	    <dd>
 	        Each <<generic-family>> keyword represents
 	        a generic font choice,
-	        and behaves as an alias for one or more locally-installed fonts
+	        and behaves as a potential alias for one or more locally-installed fonts
 	        belonging to the specified generic font category.
-	        A <<generic-family>> can thus be used as a reliable fallback
+	        A <<generic-family>> can thus be used as a fallback
 	        for when an author's more specific font choices are not available.
 
+			There are three types of generic family:
+
+			1.	Generics which apply to all Unicode characters 
+				and will <em>always</em> match a locally installed font.
+				For example, ''monospaced''.
+
+			2.	Generics which apply to all Unicode characters
+				but may not match to a locally installed font
+				on some systems.
+				For example, ''ui-rounded''.
+
+			3.	Generics which are writing-system specific,
+				only apply to a subset of Unicode characters,
+				and may not match to a locally installed font
+				on some systems.
+				For example, ''fangsong''.
+
 	        Authors are encouraged to append a generic font family as a last alternative
-	        for improved robustness.
+	        for improved robustness,
+			and to use a more specific generic font family, if applicable,
+			to prefer a specific style even if the individual named font family is not available.
+
 	        Note that <<generic-family>> keywords cannot be quoted
 	        (otherwise they are interpreted as a <<family-name>>).
 
@@ -312,10 +334,10 @@ Syntax of <<family-name>>
 	UAs must not consider these keywords as matching the <<family-name>> type.
 
 <h4 id="generic-family-name-syntax">
-Syntax of <<generic-family-name>>
+Syntax of <<generic-family>>
 </h4>
 
-	<pre class=prod><l><<generic-family-name>></l> = generic( <<custom-ident>>+ ) | <<string>> | <<custom-ident>>+</pre>
+	<pre class=prod><l><<generic-family>></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:
@@ -324,10 +346,11 @@ Syntax of <<generic-family-name>>
 			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 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.
+		and so may not match to an actual installed font on some systems;
+		but if it exists it will be an example of the requested style.
 		The third is a generic font, which is guaranteed to match on all systems.
 	</div>