XHTML validation, custom namespaces and attributes

Question

I have a website that a client requires to be XHTML valid. They check it using the W3C validator.

I want to add my own namespace and attributes so I can do things li

Answer 1

I have a website that a client requires to be XHTML valid. They check it using the W3C validator.

I've had some success with the W3C validator using, not xmlns=, but taking the standard XHTML DTD and adding a few attributes at the end as bobince describes above. I am using this to add attributes used by the PHPTAL templating system, such as

I agree that what you need is not XHTML but a superset of XHTML. However, if your client is prepared to test simply by pointing the W3C validator at your URL, then go ahead. For advice, see WDG