XXX - code marker in source code
XXX is a marker in the comments of the source code that should only be used during development to note things that need to be taken care of before a final (trunk) commit. Ideally, one should not expect to see XXXs in released software. XXX shall not be used to record new features, non-critical optimization, design changes, etc. If you want to record things like that, use TODO comments instead. People making a release shouldn't care about TODOs, but they ought to be annoyed to find XXXs.