Comment by jjuran
2 hours ago
"CarbonLib" implies Mac OS 9 (or 8) — it's the classic Mac OS implementation of the Carbon API. The OS X implementation is Carbon.framework (or more precisely, various frameworks under its umbrella).
RegisterEventHotKey() is available "in CarbonLib 1.3 and later" according to Universal Interfaces.
They moved it to HIToolbox when Carbon framework was eliminated.
This was never provided by classic Mac OS and many apps hacked it in by hooking Get/WaitNextEvent. In Carbon they didn't support this sort of "mangle the global system callbacks" shenanigans, but there was a real developer expectation of this API, and Apple was begging developers to port to Carbon. This API filled that gap.
HIToolbox still lives in /System/Library/Frameworks IIRC