docs: def set_meta_all(self, props):
          """Set metadata values for collection.
  
          ``props`` a dict with values for properties.
  
          """
          delta_props = self.get_meta()
          for key in delta_props.keys():
              if key not in props:
                  delta_props[key] = None
          delta_props.update(props)
          self.set_meta(delta_props)