I would suggest using something like comments (perhaps the standard #). These can be easily ignored by something like perldoc, but can be used as a pre-processing instruction if you want to convert to XML or any other format.

A database would take up a lot of overhead... A LOT of overhead. And require that you learn SQL. Which seems to go against reasons for not using XML (as they are both languages and have a distinct syntax e.g. DTD, XSLT, XSL-FO for XML).