ABI.FunctionSelector.encode

You're seeing just the function encode, go back to ABI.FunctionSelector module for more information.
Link to this function

encode(function_selector)

Encodes a function call signature.

Examples

iex> ABI.FunctionSelector.encode(%ABI.FunctionSelector{
...>   function: "bark",
...>   types: [
...>     {:uint, 256},
...>     :bool,
...>     {:array, :string},
...>     {:array, :string, 3},
...>     {:tuple, [{:uint, 256}, :bool]}
...>   ]
...> })
"bark(uint256,bool,string[],string[3],(uint256,bool))"