   @doc """
   Returns the tail of a list. Raises `ArgumentError` if the list is empty.
 
+  The tail of a list is the list without its first element.
+
   It works with improper lists.
 
   Allowed in guard tests. Inlined by the compiler.

  @doc """
  Returns the head of a list. Raises `ArgumentError` if the list is empty.

  It works with improper lists.

  Allowed in guard tests. Inlined by the compiler.

      tl([:one])
      #=> []

      tl([:a, :b | :improper_end])
      #=> [:b | :improper_end]

      tl([:a | %{b: 1}])
      #=> %{b: 1}
