I'm starting to use assembly and I have three issues that have come up that I
wanted to ask the TC about.

1. In <structure>, the RNC has db.structure.info as a required child of
structure. That requires structure to have either a child title element, or a child info
element containing a title. I think title and info should be optional.

I'm creating a book, so my structure has type="book". I'm including as the
first module child a reference to a file containing a book element whose only content
is an info element which contains the title, and that module has contentonly="true" so
I can discard its book wrapper. So I don't want or need a title on my structure, and
so I think it should be optional. Trying to make module the first child of structure
is currently not valid.

If I must have a structure title, what is its significance? I presume it would
be considered a label only for the structure and not appear in output. The info
element of a structure is metadata for structure, and is not to contain content for
output, right? That's what the override element is for.

2. In structure, the content model includes:

db.navigation.components*, db.module+, db.navigation.components*

That means nav elements cannot be interspersed among modules. You can't have a
toc follow a preface module, a glossary followed by a module for appendix, or an
index followed by a colophon module. Shouldn't the nav components be mixable with
modules?

3. The content model for structure includes revhistory, even though the info
element for structure allows revhistory. Is there some reason for that redundancy (the
only info element that is redundant)?