Incorrect/deprecated namespace examples

1. Change all examples of "HTML namespace" to XHTML namespace 
(http://www.w3.org/1999/xhtml). As far as I know, the "HTML namespace" 
was just a fabrication before the real XHTML namespace was available. 
Not all products will recognize the "HTML namespace".

2. (X)HTML attributes do not belong into any namespaces. Therefore 
HTML:CLASS should not cause any (X)HTML processing to happen because of 
that attribute. I propose you replace the (X)HTML attribute examples 
with XLink examples (XLink attributes are required to have a prefix).

-- 
  Heikki Toivonen