     iex> public_suffix("foo.github.io")
     "github.io"
   """
-  def public_suffix(domain, options \\ [ignore_private: false]) when is_binary(domain) do
+  @spec public_suffix(String.t) :: nil | String.t
+  @spec public_suffix(String.t, options) :: nil | String.t
+  def public_suffix(domain, options \\ []) when is_binary(domain) do
     parse_domain(domain, options, 0)
   end
 

  Comments throughout this module are direct quotes from https://publicsuffix.org/list/,
  showing how individual lines of code relate to the specification.
  """

  @doc """
  Extracts the public suffix from the provided domain based on the publicsuffix.org rules.

    "foo.github.io"
  """
  @spec registrable_domain(String.t) :: nil | String.t
  @spec registrable_domain(String.t, options) :: nil | String.t
  def registrable_domain(domain, options \\ []) when is_binary(domain) do
    # "The registered or registrable domain is the public suffix plus one additional label."
    parse_domain(domain, options, 1)
  end
