sgrep (structured grep) is a tool for searching and indexing text, SGML,XML
and HTML files and filtering text streams using structural criteria. The data
model of sgrep is based on regions, which are nonempty substrings of text.
Regions are typically occurrences of constant strings, SGML-tags, or meaningful
text elements, which are recognizable through some delimiting strings or the
builtin SGML, XML and HTML parser. Regions can be arbitrarily long, arbitrarily
overlapping, and arbitrarily nested.

Sgrep is a convenient tool for making queries to almost any kind of text files
with some well kown structure. These include programs, mail folders, news
folders, HTML, SGML, etc... With relatively simple queries you can display mail
messages by their subject or sender, extract titles or links or any regions
from HTML files, function prototypes from C or make complex queries to SGML
files based on the DTD of the file.

WWW: http://www.cs.helsinki.fi/u/jjaakkol/sgrep.html