Don't give up the dream of ImmersiveHypertextEditing just because HTML forms and plain text email are, as of 2003, the only ubiquitously deployed collaboration tools.
This business of using  style footnotes with URIs at the end of a plain text mail message is one thing, but don't do that in HTML, please. HTML is rich text. Just use links.FootNote(Within a page, you can even make your links look like footnotes, if you want.)
And let's keep the in-your-face URLs to a minimum, OK? Clean them up when you see them in this wiki.
PoorMansHypertext comes up a lot. In-program documentation like javadoc, doxygen, perl's pod, and python doc strings all seem to develop something similar (e.g. epydoc). It's a shame they're so incompatible and yet generally so similar.
Where do non-XHTML XML documents fit into the picture?