Not on the Web, but at your local bookstore. Look at Section 1.5
(pages 7-8) of
@title = "LaTeX: A Document Preparation System",
@edition = "Second",
@author = "Leslie Lamport",
@publisher = "Addison-Wesley",
@year = 1994
It gives a simple example that illustrates the advantages of semantic
markup and incidentally illustrates why you can't do semantic markup
in SGML with a fixed collection of document types.
Leslie Lamport