No 'contrib' in 'corpauthor'?

["Jean Jordaan" <jean.jordaan@gmail.com>]

Hi there

The Contrib element contains a summary or description of the
contributions made by an author, editor, or other credited source.

How come this does not include corpauthor? (contrib isn't in
corpauthor's content model).

http://www.docbook.org/tdg/en/html/contrib.html
http://www.docbook.org/tdg/en/html/corpauthor.html

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jean                                              . .. .... //\\\oo///\\