code: def _parse_control_fields(self, fields, tag_id="tag"):
          
          for field in fields:
              params = field.params
  
              # skip tags without parameters
              if tag_id not in params:
                  continue
  
              self.controlfields[params[tag_id]] = field.getContent().strip()
docs: Parse control fields.
  
          Args:
              fields (list): list of HTMLElements
              tag_id (str):  parameter name, which holds the information, about
                             field name this is normally "tag", but in case of
                             oai_marc "id".