DOCBOOK-APPS: Add new 爋mmon.element parameterentity globally?

Norman Walsh <> writes:

> / Bob Stayton <> was heard to say:
> | I started to extend the DocBook DTD to permit xi:include,
> | but I think it is kind of impossible (except for maybe
> | Norm 8^).  The xi:include element can replace *any*
> | element or group of elements, so the content models of
> | every element would get hopelessly complex.
> 
> Try adding xi:include to ndxterm.mix. It's a bit of a hack, but
> that'll allow it anywhere indexterm is allowed and that's most places.

That makes me ask: when the Grand Parameter Entity Refactoring changes
are made to the DTD, should we consider creating a new %common.element
parameter entity & making it part of the content model of every element?

(Not just for XInclude, but also because, well, who knows -- in the
future, we may need to add some other "can appear anywhere" elements.)

  --Mike