My first exposure to ‘compliance is not equivalence’.

"""POSIXLY_CORRECT (originally proposed as POSIX_ME_HARDER) is a historical environment variable used in GNU utilities to force strict compliance with the POSIX standard."""

ah, yes! https://en.wikipedia.org/wiki/Microsoft_POSIX_subsystem

the netbsd gallery (https://netbsd.org/gallery/) had a picture of somebody using that on windows xp (iirc) in order to compile pkgsrc packages in a "posix compliant" environment. the picture seem to be gone now :(