Add a "valid element" textbox to setup tinyMCE

Hi,
According to the following page:
http://tinymce.moxiecode.com/tinymce/docs/option_valid_elements.html

It is possible to initialize tinyMCE to be xhtml compliant.

But I don't know how to put this valid element option in tinyMCE.

So an interesting feature would be two textbox in the tinymce settings, one with "valid elements", the other with "invalid elements", the two main tinymce settings.

This way we could choose what elements should be valid or not.

Thanks