code: def _delete_virtual(self, key):
          
          if key not in self._virtual_keys:
              return  # Do nothing for non-virtual keys.
  
          if key in self:
              self._on_change(key, None)
          dict.__delitem__(self, key)
          self._virtual_keys.discard(key)
          for overlay in self._iter_overlays():
              overlay._delete_virtual(key)
docs: Recursively delete virtual entry. Do nothing if key is not virtual.