The devil is in the details. Consider Mark Heily's libkqueue library for Linux that emulates kqueue/kevent. Because of the way that signalfd, upon which it is built, works, code that uses kevent with signals on the BSDs has to be written one way and on Linux has to be written another. It's a subtle difference in the manual page; and it's all too easy to read the wrong implementation's manual page on the WWW (if one makes the mistake of using a search engine to find manual pages) and write things incorrectly.
It is also telling, of how difficult to interconvert it actually is in practice, that the Heily libkqueue does not implement EVFILT_AIO, EVFILT_FS, or EVFILT_PROCDESC, and implements some of the others in only a limited fashion.
It is also telling, of how difficult to interconvert it actually is in practice, that the Heily libkqueue does not implement EVFILT_AIO, EVFILT_FS, or EVFILT_PROCDESC, and implements some of the others in only a limited fashion.