How to use the elementpath.datatypes.Duration function in elementpath

'facets': [COLLAPSE_WHITE_SPACE_ELEMENT],
        'to_python': datatypes.GregorianMonthDay.fromstring,
    },  # MM-DD
    {
        'name': XSD_TIME,
        'python_type': (unicode_type, str, datatypes.Time),
        'admitted_facets': DATETIME_FACETS,
        'facets': [COLLAPSE_WHITE_SPACE_ELEMENT],
        'to_python': datatypes.Time.fromstring,
    },  # hh:mm:ss
    {
        'name': XSD_DURATION,
        'python_type': (unicode_type, str, datatypes.Duration),
        'admitted_facets': FLOAT_FACETS,
        'facets': [COLLAPSE_WHITE_SPACE_ELEMENT],
        'to_python': datatypes.Duration.fromstring,
    },  # PnYnMnDTnHnMnS

    # Other primitive types
    {
        'name': XSD_QNAME,
        'python_type': (unicode_type, str),
        'admitted_facets': STRING_FACETS,
        'facets': [COLLAPSE_WHITE_SPACE_ELEMENT, qname_validator],
    },  # prf:name (the prefix needs to be qualified with an in-scope namespace)
    {
        'name': XSD_NOTATION_TYPE,
        'python_type': (unicode_type, str),
        'admitted_facets': STRING_FACETS,
        'facets': [COLLAPSE_WHITE_SPACE_ELEMENT],
    },  # type for NOTATION attributes: QNames of xs:notation declarations as value space.
    {

'name': XSD_GMONTH_DAY,
        'python_type': (unicode_type, str, datatypes.GregorianMonthDay),
        'admitted_facets': DATETIME_FACETS,
        'facets': [COLLAPSE_WHITE_SPACE_ELEMENT],
        'to_python': datatypes.GregorianMonthDay.fromstring,
    },  # MM-DD
    {
        'name': XSD_TIME,
        'python_type': (unicode_type, str, datatypes.Time),
        'admitted_facets': DATETIME_FACETS,
        'facets': [COLLAPSE_WHITE_SPACE_ELEMENT],
        'to_python': datatypes.Time.fromstring,
    },  # hh:mm:ss
    {
        'name': XSD_DURATION,
        'python_type': (unicode_type, str, datatypes.Duration),
        'admitted_facets': FLOAT_FACETS,
        'facets': [COLLAPSE_WHITE_SPACE_ELEMENT],
        'to_python': datatypes.Duration.fromstring,
    },  # PnYnMnDTnHnMnS

    # Other primitive types
    {
        'name': XSD_QNAME,
        'python_type': (unicode_type, str),
        'admitted_facets': STRING_FACETS,
        'facets': [COLLAPSE_WHITE_SPACE_ELEMENT, qname_validator],
    },  # prf:name (the prefix needs to be qualified with an in-scope namespace)
    {
        'name': XSD_NOTATION_TYPE,
        'python_type': (unicode_type, str),
        'admitted_facets': STRING_FACETS,