code: def promote(self, content):
          
          for n, v in content.data:
              if isinstance(v, list):
                  content.data = v
                  return
          content.data = []
docs: Promote (replace) the content.data with the first attribute
          of the current content.data that is a I{list}.  Note: the
          content.data may be empty or contain only _x attributes.
          In either case, the content.data is assigned an empty list.
          @param content: An array content.
          @type content: L{Content}