> I must have some way of indicating
> to the application where I want white space, or I do not have
> sufficient control over the formatting of my documents.
Sorry, you're not supposed to have control over the formatting of your
documents, in the sense that I think you mean. (I may be
misinterpreting your meaning; could you say a bit more about why
"whitespace in general is *not* purely presentational"?) There are
plenty of formats that support that kind of thing; there's no need to
turn HTML into yet-another-bastardized-procedural-markup format.
I think it's pretty clear, though, that there's a lot of desire for
browsers like XMosaic to support both HTML and one or more additional
procedural formats, such as TeX or MS-Word.