if you are an SGML purist, you are going to mark up your document
in a format that's semantically correct (chapters are chapters,
paragraphs are paragraphs, and that blob of white space is a
carefully constructed signifier of an emphatic pause).
you then take your SGML document and transmute it into another SGML
document, one with a simpler format and more concrete representation.
in the World Wide Web you make the decision that <chapter> means
<h1>, text inside <sidenote> should be marked as such to show up as
you want it on screen, etc etc.
lots of people are going to do lots of browsers. you have to pick
which one you expect things to look "best" in and work to that. you
may want to generate text for paper, in which case your original markup
may get transmuted into a different format for the paper layout.
the "transmute" step is one people seem to be missing. i would like
to see more tools thought through that generate HTML as an output
of another process which starts with a richer document model.
--Ed