I would like to add bibl, author, title (and probably editor and series)
markup to a real book which contains loose references. As long as author
and title are mentioned together, no problem.

The first case that can't be handled easily is when the author is
mentioned in the text and the title in a footnote, leading to
    <title>About ...</title>
which is still legal.

However, as soon as there is more text between the author and the
footnote mark, with markup that's not a children of bibl; or as soon
as the footnote mentions an editor, this will fail because title and
author can be children of note but not editor. 

A different way to handle this could be adding the author name near
the title, just for the purpose of the bibl, within the footnote, but
not rendering it. Is there fitting markup for such non-rendered
additions? Is it simply <author rend='none'> and let the rendering
backend worry about it?

Please give me a hint on how to handle such loose bibliographic

R Stephan