'Return a new |_ContentTypeMap| instance populated with the contents
of *content_types_xml*.'

@staticmethod
def from_xml(content_types_xml):

    types_elm = parse_xml(content_types_xml)
    ct_map = _ContentTypeMap()
    for o in types_elm.overrides:
        ct_map._add_override(o.partname, o.content_type)
    for d in types_elm.defaults:
        ct_map._add_default(d.extension, d.content_type)
    return ct_map
