Sourcehighlightide is an IDE for GNU Source-highlight (given a source file, produces a document with syntax highlighting); in particular, it is useful when you have to develop a new language definition file for source-highlight (Source-highlight reads source language specifications dynamically, thus it can be easily extended (without recompiling the sources) for handling new languages), modify an existing one, and, most importantly, debug a language definition file.
Sourcehighlightide home page is http://srchighliteide.sourceforge.net.