I'm not totally sure we need it, but I use it in the MoinMoin plugin (because moin needs it) and I figured out I'll describe it. Actually, this proposition is different from what I use for moin -- the shebang is on the same line as the opening braces, whil in my plugin it is located on the next line. The reason is simple: if I made it on the same line in moin, the page text would be incompatible with Creole.
Not sure about the naming convention too. It seems right to move away from the engine's plugin naming convention and avoid things like "ceeplusplus" or "ceesharp" when there is nothing preventing us from writing "c++" or "c#". We should probably decide wether to ignore character case, though. In case of conflict with the internal plugin naming conventions (no "#" or "+" allowed in the plugin names, for example), a translation table can be used internally.
Other solution would be similar to how macros and other extensions are to be handled -- leave the naming as the responsibility of the engine developer/wiki admin, gaining some flexibility and ease of implementation but losing interoperability.
There is also a problem of using this markup for things different than just syntax highlighting -- for example, MoinMoin has a CSV plugin that will render the codeas a table. There is also a similar LaTeX extension. Technically, they would belong to the "macro and plugins" category, so should be done using "" or whatever else we (or the engine developer) decides on. Then again, one can argue that they only improve the presentation of the data -- something similar to syntax highlighting.
-- Radomir Dopieralski, 2007-Mar-24