On a closer read, the comment mentions plan9's arg(3): https://9fans.github.io/plan9port/man/man3/arg.html https://9fans.github.io/plan9port/man/man3/arg.html

On a closer read, the comment mentions plan9's arg(3): https://9fans.github.io/plan9port/man/man3/arg.html https://9fans.github.io/plan9port/man/man3/arg.html Generally, I think it's pretty normal to interpret "POSIX compliant" as a minimum requirement, and then extend that to your own whims as long as you don't break the POSIX part.