docs: def from_parts(cls, parts):
          """
          Return content types XML mapping each part in *parts* to the
          appropriate content type and suitable for storage as
          ``[Content_Types].xml`` in an OPC package.
          """
          cti = cls()
          cti._defaults['rels'] = CT.OPC_RELATIONSHIPS
          cti._defaults['xml'] = CT.XML
          for part in parts:
              cti._add_content_type(part.partname, part.content_type)
          return cti