There are several problems between Crossmark and Creole that are much harder and more complicated than described here. First of all, you claim that there are only few incompatiblities, but this is obviously untrue. There are few problems if you want to use Crossmark-formatted documents in Creole-compatible wikis, that's true. But there are many, many troubles if you try to do it the other way around. To just name the few:

* Crossmark has very unforgiving markup for lists, reuiring 4-space indentation per level and various whitespaces. Implementing it in Creole would make MixedMode impossible.
* Crossmark uses indetation for syntax.
* Crossmark requires the trailing equal signs in headings.
* Crossmark's emphasis markup is extremely complicated and, I'm afraid, incompatible in most corner cases with Creole.
* Crossmark __requires__ a number of features, such as specific macros, that are intentionally left unhandled in Creole.
* Creole doesn't have markup for monospace text.
* Crossmark's markup uses english words. This is impossible for Creole.
* Crossmark's heading markup conflicts with Creole's horizontal line markup.

I think that forcing Creole to be compatible with Crossmark would render it pretty much unusable for wikis -- especially in MixedMode.

Btw. Crossmark __used to be__ much more compatible with Creole, but undergo a number of pretty arbitrary changes (like the link syntax, for example).

-- [RadomirDopieralski], 2007-01-18