IP.is_ipv4

You're seeing just the macro is_ipv4, go back to IP module for more information.

true if the argument is an ipv4 datatype

usable in guards.

iex> IP.is_ipv4({10, 0, 0, 1})
true
iex> IP.is_ipv4(:foo)
false
iex> IP.is_ipv4({256, 0, 0, 0})
false