code: def _find_header_flat(self):
          
          nodes = self._node.contents.filter_tags(
                      matches=ftag('th'), recursive=False)
          if not nodes:
              return
          self._log('found header outside rows (%d <th> elements)' % len(nodes))
          return nodes
docs: Find header elements in a table, if possible. This case handles
          situations where '<th>' elements are not within a row('<tr>')