Mac OS X Leopard - Technology - UNIX.In:Leopard Technology Overview.Apple Inc.,abgerufen am 11.Juni 2007:„Leopard is now an Open Brand UNIX 03 Registered Product, conforming to the SUSv3 and POSIX 1003.1 specifications for the C API, Shell Utilities, and Threads.“
Open Group Base Specifications Issue 7, 2008 edition.The Open Group,abgerufen am 29.August 2018(The _POSIX_C_SOURCE Feature Test Macro):„Note that the definition of _XOPEN_SOURCE with the value 700 makes the definition of _POSIX_C_SOURCE redundant and it can safely be omitted.“