@ Martin

   [quote]You've clearly done a huge amount of homework before asking this question![/quote]

Am feeling like there is so much homework still to do! I really want to limit the cost and wasted time of heading down the wrong path.

It is also clear to me that I have plenty more work to do to better understand how to make use of multiple schema. Perhaps the subject of a future post.

    [quote]...the single biggest advantage of using TEI as a base format in a scenario such as the one you outline is that it covers a huge range of use-cases.[/quote]

The main factors that initially drew me to TEI include:

- open, non-proprietary schema (I originally came across Scribe - ScML - and went looking for an "open source" alternative)
- deep history and community involvement/vibrancy (there is obviously an enormous amount of intellectual capital amongst the TEI community when it comes to markup and text encoding)
- access to relevant tools (generally a function of the above 2 factors)

A quick review of the guidelines showed the breadth of the schema. As you have noted, although the TEI's history is linked to humanities, and many schema offer to ability to extend the schema, the standard schema cover many use cases and embedding additional namespaces adds even more.

    [quote]TEI ... is ready to handle everything[/quote]

This is consistent with my thinking that the base format must be one of the more generic schema capable of handling many document types either natively or by being extended/customized/specialized - ie one that provides core components such as metadata and structure, alongside which other, more specialized modules can be added.

It is also one of the main reasons why I am considering TEI as one of the options to use as the base format. It seems like a fairly obvious choice, although the OP was aimed at helping me (and others) consider other viable alternatives and the factors involved in making that choice.

Would I be correct in stating that the 2 most generic schema out of those I mentioned in my OP include TEI and XHTML?