1	POSIX.1-1990 (includes POSIX.1-1988, implies C89)
2	POSIX.1-1990 plus POSIX.2-1992
199309	POSIX.1b-1993 (includes POSIX.1-1990)
199506	POSIX.1-1996
200112	POSIX.1-2001 (implies C99)
200809	POSIX.1-2008 (implies C99)