How to use the stix2.properties.ReferenceProperty function in stix2

('type', TypeProperty(_type)),
        ('spec_version', StringProperty(fixed='2.1')),
        ('id', IDProperty(_type, spec_version='2.1')),
        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.1')),
        ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('object_ref', ReferenceProperty(valid_types=["SCO", "SDO", "SRO"], spec_version='2.1', required=True)),
        # TODO: 'object_modified' it MUST be an exact match for the modified time of the STIX Object (SRO or SDO) being referenced.
        ('object_modified', TimestampProperty(precision='millisecond')),
        # TODO: 'contents' https://docs.google.com/document/d/1ShNq4c3e1CkfANmD9O--mdZ5H0O_GLnjN28a_yrEaco/edit#heading=h.cfz5hcantmvx
        ('contents', DictionaryProperty(spec_version='2.1', required=True)),
        ('revoked', BooleanProperty()),
        ('labels', ListProperty(StringProperty)),
        ('confidence', IntegerProperty()),
        ('external_references', ListProperty(ExternalReference)),
        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.1'))),
        ('granular_markings', ListProperty(GranularMarking)),
    ])


class TLPMarking(_STIXBase):
    # TODO: Add link
    """For more detailed information on this object's properties, see
    `the STIX 2.1 specification `__.
    """

    _type = 'tlp'
    _properties = OrderedDict([
        ('tlp', StringProperty(required=True)),
    ])

raise ValueError("must be a Statement, TLP Marking or a registered marking.")


class MarkingDefinition(_STIXBase, _MarkingsMixin):
    """For more detailed information on this object's properties, see
    `the STIX 2.0 specification `__.
    """

    _type = 'marking-definition'
    _properties = OrderedDict([
        ('type', TypeProperty(_type)),
        ('id', IDProperty(_type)),
        ('created_by_ref', ReferenceProperty(type='identity')),
        ('created', TimestampProperty(default=lambda: NOW)),
        ('external_references', ListProperty(ExternalReference)),
        ('object_marking_refs', ListProperty(ReferenceProperty(type='marking-definition'))),
        ('granular_markings', ListProperty(GranularMarking)),
        ('definition_type', StringProperty(required=True)),
        ('definition', MarkingProperty(required=True)),
    ])

    def __init__(self, **kwargs):
        if set(('definition_type', 'definition')).issubset(kwargs.keys()):
            # Create correct marking type object
            try:
                marking_type = OBJ_MAP_MARKING[kwargs['definition_type']]
            except KeyError:
                raise ValueError("definition_type must be a valid marking type")

            if marking_type == TLPMarking:
                # TLP instances in the spec have millisecond precision unlike other markings
                self._properties = copy.deepcopy(self._properties)

('content_type', StringProperty()),
        ('from_ref', ReferenceProperty(valid_types='email-addr', spec_version='2.1')),
        ('sender_ref', ReferenceProperty(valid_types='email-addr', spec_version='2.1')),
        ('to_refs', ListProperty(ReferenceProperty(valid_types='email-addr', spec_version='2.1'))),
        ('cc_refs', ListProperty(ReferenceProperty(valid_types='email-addr', spec_version='2.1'))),
        ('bcc_refs', ListProperty(ReferenceProperty(valid_types='email-addr', spec_version='2.1'))),
        ('message_id', StringProperty()),
        ('subject', StringProperty()),
        ('received_lines', ListProperty(StringProperty)),
        ('additional_header_fields', DictionaryProperty(spec_version='2.1')),
        ('body', StringProperty()),
        ('body_multipart', ListProperty(EmbeddedObjectProperty(type=EmailMIMEComponent))),
        ('raw_email_ref', ReferenceProperty(valid_types='artifact', spec_version='2.1')),
        ('extensions', ExtensionsProperty(spec_version='2.1', enclosing_type=_type)),
        ('spec_version', StringProperty(fixed='2.1')),
        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.1'))),
        ('granular_markings', ListProperty(GranularMarking)),
        ('defanged', BooleanProperty(default=lambda: False)),
    ])
    _id_contributing_properties = ["from_ref", "subject", "body"]

    def _check_object_constraints(self):
        super(EmailMessage, self)._check_object_constraints()
        self._check_properties_dependency(['is_multipart'], ['body_multipart'])
        if self.get('is_multipart') is True and self.get('body'):
            # 'body' MAY only be used if is_multipart is false.
            raise DependentPropertiesError(self.__class__, [('is_multipart', 'body')])


class ArchiveExt(_Extension):
    # TODO: Add link
    """For more detailed information on this object's properties, see

"""

    _invalid_source_target_types = ['bundle', 'language-content', 'marking-definition', 'relationship', 'sighting']

    _type = 'relationship'
    _properties = OrderedDict([
        ('type', TypeProperty(_type)),
        ('spec_version', StringProperty(fixed='2.1')),
        ('id', IDProperty(_type, spec_version='2.1')),
        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.1')),
        ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('relationship_type', StringProperty(required=True)),
        ('description', StringProperty()),
        ('source_ref', ReferenceProperty(invalid_types=_invalid_source_target_types, spec_version='2.1', required=True)),
        ('target_ref', ReferenceProperty(invalid_types=_invalid_source_target_types, spec_version='2.1', required=True)),
        ('start_time', TimestampProperty()),
        ('stop_time', TimestampProperty()),
        ('revoked', BooleanProperty(default=lambda: False)),
        ('labels', ListProperty(StringProperty)),
        ('confidence', IntegerProperty()),
        ('lang', StringProperty()),
        ('external_references', ListProperty(ExternalReference)),
        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.1'))),
        ('granular_markings', ListProperty(GranularMarking)),
    ])

    # Explicitly define the first three kwargs to make readable Relationship declarations.
    def __init__(
        self, source_ref=None, relationship_type=None,
        target_ref=None, **kwargs
    ):

('id', IDProperty(_type, spec_version='2.1')),
        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.1')),
        ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('relationship_type', StringProperty(required=True)),
        ('description', StringProperty()),
        ('source_ref', ReferenceProperty(invalid_types=_invalid_source_target_types, spec_version='2.1', required=True)),
        ('target_ref', ReferenceProperty(invalid_types=_invalid_source_target_types, spec_version='2.1', required=True)),
        ('start_time', TimestampProperty()),
        ('stop_time', TimestampProperty()),
        ('revoked', BooleanProperty(default=lambda: False)),
        ('labels', ListProperty(StringProperty)),
        ('confidence', IntegerProperty()),
        ('lang', StringProperty()),
        ('external_references', ListProperty(ExternalReference)),
        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.1'))),
        ('granular_markings', ListProperty(GranularMarking)),
    ])

    # Explicitly define the first three kwargs to make readable Relationship declarations.
    def __init__(
        self, source_ref=None, relationship_type=None,
        target_ref=None, **kwargs
    ):
        # Allow (source_ref, relationship_type, target_ref) as positional args.
        if source_ref and not kwargs.get('source_ref'):
            kwargs['source_ref'] = source_ref
        if relationship_type and not kwargs.get('relationship_type'):
            kwargs['relationship_type'] = relationship_type
        if target_ref and not kwargs.get('target_ref'):
            kwargs['target_ref'] = target_ref

def wrapper(cls):
        _properties = list(itertools.chain.from_iterable([
            [
                ('type', TypeProperty(type)),
                ('id', IDProperty(type, spec_version='2.0')),
                ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.0')),
                ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
                ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),
            ],
            [x for x in properties if not x[0].startswith('x_')],
            [
                ('revoked', BooleanProperty(default=lambda: False)),
                ('labels', ListProperty(StringProperty)),
                ('external_references', ListProperty(ExternalReference)),
                ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.0'))),
                ('granular_markings', ListProperty(GranularMarking)),
            ],
            sorted([x for x in properties if x[0].startswith('x_')], key=lambda x: x[0]),
        ]))
        return _custom_object_builder(cls, type, _properties, '2.0')
    return wrapper

msg = "{0.id} 'stop_time' must be later than 'start_time'"
            raise ValueError(msg.format(self))


class Sighting(STIXRelationshipObject):
    # TODO: Add link
    """For more detailed information on this object's properties, see
    `the STIX 2.1 specification `__.
    """

    _type = 'sighting'
    _properties = OrderedDict([
        ('type', TypeProperty(_type)),
        ('spec_version', StringProperty(fixed='2.1')),
        ('id', IDProperty(_type, spec_version='2.1')),
        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.1')),
        ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('description', StringProperty()),
        ('first_seen', TimestampProperty()),
        ('last_seen', TimestampProperty()),
        ('count', IntegerProperty(min=0, max=999999999)),
        ('sighting_of_ref', ReferenceProperty(valid_types="SDO", spec_version='2.1', required=True)),
        ('observed_data_refs', ListProperty(ReferenceProperty(valid_types='observed-data', spec_version='2.1'))),
        ('where_sighted_refs', ListProperty(ReferenceProperty(valid_types='identity', spec_version='2.1'))),
        ('summary', BooleanProperty()),
        ('revoked', BooleanProperty(default=lambda: False)),
        ('labels', ListProperty(StringProperty)),
        ('confidence', IntegerProperty()),
        ('lang', StringProperty()),
        ('external_references', ListProperty(ExternalReference)),
        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.1'))),

`the STIX 2.0 specification `__.
    """

    _type = 'course-of-action'
    _properties = OrderedDict([
        ('type', TypeProperty(_type)),
        ('id', IDProperty(_type, spec_version='2.0')),
        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.0')),
        ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('name', StringProperty(required=True)),
        ('description', StringProperty()),
        ('revoked', BooleanProperty(default=lambda: False)),
        ('labels', ListProperty(StringProperty)),
        ('external_references', ListProperty(ExternalReference)),
        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.0'))),
        ('granular_markings', ListProperty(GranularMarking)),
    ])


class Identity(STIXDomainObject):
    """For more detailed information on this object's properties, see
    `the STIX 2.0 specification `__.
    """

    _type = 'identity'
    _properties = OrderedDict([
        ('type', TypeProperty(_type)),
        ('id', IDProperty(_type, spec_version='2.0')),
        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.0')),
        ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),

class LanguageContent(_STIXBase):
    # TODO: Add link
    """For more detailed information on this object's properties, see
    `the STIX 2.1 specification `__.
    """

    _type = 'language-content'
    _properties = OrderedDict([
        ('type', TypeProperty(_type)),
        ('spec_version', StringProperty(fixed='2.1')),
        ('id', IDProperty(_type, spec_version='2.1')),
        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.1')),
        ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),
        ('object_ref', ReferenceProperty(valid_types=["SCO", "SDO", "SRO"], spec_version='2.1', required=True)),
        # TODO: 'object_modified' it MUST be an exact match for the modified time of the STIX Object (SRO or SDO) being referenced.
        ('object_modified', TimestampProperty(precision='millisecond')),
        # TODO: 'contents' https://docs.google.com/document/d/1ShNq4c3e1CkfANmD9O--mdZ5H0O_GLnjN28a_yrEaco/edit#heading=h.cfz5hcantmvx
        ('contents', DictionaryProperty(spec_version='2.1', required=True)),
        ('revoked', BooleanProperty()),
        ('labels', ListProperty(StringProperty)),
        ('confidence', IntegerProperty()),
        ('external_references', ListProperty(ExternalReference)),
        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.1'))),
        ('granular_markings', ListProperty(GranularMarking)),
    ])


class TLPMarking(_STIXBase):
    # TODO: Add link
    """For more detailed information on this object's properties, see

super(ExternalReference, self)._check_object_constraints()
        self._check_at_least_one_property(["description", "external_id", "url"])


class KillChainPhase(_STIXBase):
    _properties = OrderedDict()
    _properties.update([
        ('kill_chain_name', StringProperty(required=True)),
        ('phase_name', StringProperty(required=True)),
    ])


class GranularMarking(_STIXBase):
    _properties = OrderedDict()
    _properties.update([
        ('marking_ref', ReferenceProperty(required=True, type="marking-definition")),
        ('selectors', ListProperty(SelectorProperty, required=True)),
    ])


class TLPMarking(_STIXBase):
    _type = 'tlp'
    _properties = OrderedDict()
    _properties.update([
        ('tlp', Property(required=True))
    ])


class StatementMarking(_STIXBase):
    _type = 'statement'
    _properties = OrderedDict()
    _properties.update([