
  [;1m-spec is_boolean(Term) -> boolean() when Term :: term().[0m

  Returns [;;4mtrue[0m if [;;4mTerm[0m is the atom [;;4mtrue[0m or the atom [;;4mfalse[0m
  (that is, a boolean). Otherwise returns [;;4mfalse[0m.

  Allowed in guard tests.
