While I agree it should be more obvious, it does say in the opening section:
> Those functions that are specific to gawk are marked with a pound sign (‘#’). They are not available in compatibility mode (see section Command-Line Options)
Oh dear lord. I've looked at that page probably twenty times in the past year and still not seen the note about that pound sign. Thanks for pointing it out. Man it's infuriating.
> Those functions that are specific to gawk are marked with a pound sign (‘#’). They are not available in compatibility mode (see section Command-Line Options)