use of XML to encode linguistic structures

I'm interested in the use of XML to encode natural language structures (to
facilitate easy electronic processing of internet documents). See for
example, "the problem" and "the solution" at the following URL:

(sorry if it's a little bit corny! ...that's a story I won't bore you with)

http://people.we.mediaone.net/wallyflint/picturelanguage/revolution.html

Just wondering if anyone can point me to resources describing the
development of this kind of technology.