From phpBB Development Wiki
Support for extensible BBCode will be required. Maybe we can add parsers for other languages, such as wiki style markup.
Has to be extensible and stack based. Can be based on the parser for Ascraeus. Should support caching of the structure so content does not need to be parsed on viewing. Reparsing old posts after changing the BBCode configuration/definition should be simple, however that might be related to how formatted text is stored in the database.