Specifically defined by POSIX: https://pubs.opengroup.org/onlinepubs/9699919799/functions/g...

Funny how that goes: macOS is POSIX certified but no other desktop BSD or Linux is.

There have been POSIX-certified Linux variants. But the open source projects you use don't bother (for obvious reasons) and commercial derivatives like Android and ChromeOS don't need it. Similarly Window NT was POSIX-certified way back in the day yet its descendants aren't, even though they implement the same API set (via very different technology).

Because it's an expensive and lengthy process. And every version would need to be re-certified.

According to https://www.opengroup.org/openbrand/register/ macOS 15 is not certified.

It's POSIX which Apple generally abides by except for timer_create. macOS is historically officially a UNIX, which would require getaddrinfo.

it is apparently on Mac and arguably with good reason. See this comment https://news.ycombinator.com/item?id=41572770