'Declare that other types may be converted to this property type.
Args:
tp (Property) :
A type that may be converted automatically to this property
type.
converter (callable) :
A function accepting ``value`` to perform conversion of the
value to this property type.
Returns:
self'

def accepts(self, tp, converter):

    tp = ParameterizedProperty._validate_type_param(tp)
    self.alternatives.append((tp, converter))
    return self
