docs: def boolean(_object):
      """
      Validates a given input is of type boolean.
  
      Example usage::
  
          data = {'a' : True}
          schema = ('a', boolean)
  
      You can also use this as a decorator, as a way to check for the
      input before it even hits a validator you may be writing.
  
      .. note::
          If the argument is a callable, the decorating behavior will be
          triggered, otherwise it will act as a normal function.
  
      """
      if is_callable(_object):
          _validator = _object
  
          @wraps(_validator)
          def decorated(value):
              ensure(isinstance(value, bool), "not of type boolean")
              return _validator(value)
          return decorated
      ensure(isinstance(_object, bool), "not of type boolean")