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.