Fix w3c#2721

Author: svgeesus

css-fonts-4/Overview.bs

@@ -126,13 +126,13 @@ There are two types of font family names:
 <dl>
 	<dt><dfn id="family-name-value"><<family-name>></dfn>
 	<dd>
-		The name of a font family of choice such as Helvetica or Verdana in the previous example.
+		The name of a font family of choice, such as Helvetica or Verdana in the previous example.
 
 	<dt><dfn id="generic-family-value"><<generic-family>></dfn>
 	<dd>
-		The following generic family keywords are defined: ''serif'', ''sans-serif'', ''cursive'',
-		''fantasy'', and ''monospace''. These keywords can be used as a general fallback mechanism
-		when an author's desired font choices are not available.  As keywords, they must not
+		The following generic family keywords are defined: ''serif'', ''sans-serif'', ''cursive'', ''fantasy'',  ''monospace'', ''system-ui'', ''emoji'', ''math'' and ''fangsong''.
+		These keywords can be used as a general fallback mechanism
+		when an author's desired font choices are not available.  As keywords, they <em>must not</em>
 		be quoted. Authors are encouraged to append a generic font family as a last alternative for
 		improved robustness.
 	</dl>