[CSS22] Refer to XML 1.1 instead of XML 1.0.

Author: bert-github

css2/intro.src

@@ -179,7 +179,7 @@ element are three times wider than the font size.
 <p>This section is non-normative.
 
 <P>CSS can be used with any structured document format, for example
-with applications of the eXtensible Markup Language [[-XML10]]. In
+with applications of the eXtensible Markup Language [[-XML11]]. In
 fact, XML depends more on style sheets than HTML, since authors can
 make up their own elements that user agents do not know how to
 display.