IP.is_ip

You're seeing just the macro is_ip, go back to IP module for more information.

true if the argument is either ipv6 or ipv4 datatype

usable in guards.

iex> IP.is_ip({0, 0, 0, 0, 0, 0, 0, 1})
true
iex> IP.is_ip({127, 0, 0, 1})
true