Why does xs:extension not support a user-defined datatype

The Taminio documentation states:

The base attribute of xs:extension may not refer to a user-defined datatype, only to pre-defined types.

http://servline24.softwareag.com/SecuredServices/document//java/ins421win/Documentation/tslref/nsxmlschema.htm#spyanchor0

Why is this not supported and what is the work around for this?

I want to declare a datatype ?docDetails? that will store meta data based upon what document it is describing. Since each different type of document will need a different description I wanted to create multiple complexTypes based off the docDetails that can be used depending on the document. Any help in solving this would be appreciated.

Thanks

Well I figured out how to handle this, I just used a “choice” statemnent. Seems like a newbie mistake.

I am still interested to see if Tamino has an answer for code reuse. I’m sure I’ll find something as I go through all of the documentation.