DOCBOOK: DTD Customization

[Guillaume Rouchy <rouchyg@gatwick.geco-prakla.slb.com>]

Hello,

I built a small application that allow the user to author a docbook
document by filling a template. In order to mark the data written by the
user into the document, I was thinking about using a new tag, <user> for
instance.
This tag can only contain CDATA but may appear in ANY context (<title>,
<para>, <email>, etc...).
How can I modify the DTD to reflect that ? I hope there is another way
than changing every element declaration to include the new tag...

Thanks for your help.

Guillaume