[css-fonts-4] Add emoji as a keyword to unicode‑range w3c#4573

Author: svgeesus

css-fonts-4/Overview.bs

@@ -2816,7 +2816,7 @@ Character range: the 'unicode-range!!descriptor' descriptor</h3>
 
 <pre class='descdef'>
 Name: unicode-range
-Value: <<urange>>#
+Value: [ <<urange>> || ''@font-face/unicode-range/emoji'' ]#
 Initial: U+0-10FFFF
 For: @font-face
 </pre>
@@ -2830,7 +2830,17 @@ For: @font-face
 This descriptor defines the set of Unicode codepoints that may be
 supported by the font face for which it is declared. The descriptor
 value is a comma-delimited list of Unicode range (<<urange>>)
-values. The union of these ranges defines the set of codepoints that
+values. 
+
+In addition, the keyword
+<dfn for="@font-face/unicode-range">emoji</dfn>
+may be added to the list.
+It is shorthand for a Unicode range
+which includes all characters
+which have <a href="http://www.unicode.org/reports/tr51/#Emoji_Properties">the emoji property</a>
+[[UTS51]].
+
+The union of these ranges defines the set of codepoints that
 serves as a hint for user agents when deciding whether or not to
 download a font resource for a given text run.