The general apple documentation for functions, etc appears to be pretty much a customized doxygen. One can see this by reading the header files for some of their frameworks and noting the doxygen comments there match up with their web-published documentation exactly.

That said: some folks didn't really get the memo, because there are important details that are sometimes included in non-doxygen comments in Apple's headers and thus aren't reproduced into Apple's generated/published docs.

In particular, the headers (sometimes) include annotations for specific types included in CF containers for return values.