Index: source
===================================================================
--- source	(revision 2062)
+++ source	(revision 2063)
@@ -5814,13 +5814,24 @@
   well as elements in other namespaces if the relevant specifications
   allow it (in particular, MathML and SVG allow <code
   title="attr-xml-lang">xml:lang</code> attributes to be specified on
-  their elements). Authors must not use the <code
-  title="attr-xml-lang">xml:lang</code> attribute in <span>HTML
-  documents</span>. If both the <code title="attr-lang">lang</code>
+  their elements). If both the <code title="attr-lang">lang</code>
   attribute and the <code title="attr-xml-lang">xml:lang</code>
   attribute are specified on the same element, they must have exactly
   the same value.</p>
 
+  <p>Authors must not use the <code
+  title="attr-xml-lang">xml:lang</code> attribute (that is, the <code
+  title="">lang</code> attribute with the <code title="">xml</code>
+  prefix in the <code
+  title="">http://www.w3.org/XML/1998/namespace</code> namespace) in
+  <span>HTML documents</span>. To ease migration to and from XHTML,
+  authors may specify an attribute in no namespace with no prefix and
+  with the localname <code title="">xml:lang</code> on <span>HTML
+  elements</span> in <span>HTML documents</span>, but such attributes
+  must only be specified if a <code title="attr-lang">lang</code>
+  attribute is also specified, and both attributes must have the same
+  value.</p>
+
   <hr>
 
   <p>To determine the language of a node, user agents must look at the