In the context of option parsing, "POSIX compliant" makes me think of the semantics of getopt(3): https://pubs.opengroup.org/onlinepubs/9699919799/functions/get

In the context of option parsing, "POSIX compliant" makes me think of the semantics of getopt(3): https://pubs.opengroup.org/onlinepubs/9699919799/functions/getopt.html https://pubs.opengroup.org/onlinepubs/9699919799/functions/g... Notably, the utility conventions and even the guidelines (guideline 14 presumes non-compliance with guideline 7) support optional option-arguments, while the bundling semantics of getopt preclude optional option-arguments. Utilities, including POSIX-defined utilities, which have optional option-arguments cannot use getopt.