[CSS22] Added bibliographic reference for CSS Snapshot.

Author: bert-github

css2/refs.src

@@ -144,6 +144,14 @@ charset values from <A
 href="http://www.iana.org/assignments/character-sets">
 http://www.iana.org/assignments/character-sets</A>. </DD>
 
+<dt><strong><a name="ref-CSS" class="informref">[CSS]</a></strong>
+<dd>"CSS Snapshot", Tab Atkins Jr., Elika J. Etemad (fantasai),
+Florian Rivoal, 13 October 2015<br>
+<a href="http://www.w3.org/TR/2015/NOTE-css-2015-20151013/">
+http://www.w3.org/TR/2015/NOTE-css-2015-20151013/</a> or a later
+version. The latest version is available at <a
+href="http://www.w3.org/TR/CSS/">http://www.w3.org/TR/CSS/</a>
+
 <dt><strong><a name="ref-CSS1" class="informref">[CSS1]</a></strong>
 <dd>"Cascading Style Sheets, level 1", H. W. Lie and B. Bos,
 17 December 1996, revised 11 January 1999<BR>