code: def _field(self, *keys) -> Any:
          
          try:
              d = self._node
              for key in keys:
                  d = d[key]
              return d
          except KeyError:
              d = self._full_metadata
              for key in keys:
                  d = d[key]
              return d
docs: Lookups given fields in _node, and if not found in _full_metadata. Raises KeyError if not found anywhere.