Kernel.is_map_key

You're seeing just the function is_map_key, go back to Kernel module for more information.

is_map_key(map, key)

(since 1.10.0)

is_map_key(map(), term()) :: boolean()

Returns true if key is a key in map; otherwise returns false.

It raises BadMapError if the first element is not a map.

Allowed in guard tests. Inlined by the compiler.