code: def from_xml(content_types_xml):
          
          types_elm = parse_xml(content_types_xml)
          ct_map = _ContentTypeMap()
          for o in types_elm.override_lst:
              ct_map._add_override(o.partName, o.contentType)
          for d in types_elm.default_lst:
              ct_map._add_default(d.extension, d.contentType)
          return ct_map
docs: Return a new |_ContentTypeMap| instance populated with the contents
          of *content_types_xml*.