Index: Sanitizer.php
===================================================================
--- Sanitizer.php	(revision 45716)
+++ Sanitizer.php	(working copy)
@@ -40,10 +40,11 @@
  * Allows some... latitude.
  * Used in Sanitizer::fixTagAttributes and Sanitizer::decodeTagAttributes
  */
-$attrib = '[A-Za-z0-9]';
+$attrib_first = '[:A-Z_a-z]';
+$attrib = '[:A-Z_a-z-.0-9]';
 $space = '[\x09\x0a\x0d\x20]';
 define( 'MW_ATTRIBS_REGEX',
-	"/(?:^|$space)($attrib+)
+	"/(?:^|$space)({$attrib_first}{$attrib}*)
 	  ($space*=$space*
 		(?:
 		 # The attribute value: quoted or alone