code: def reference(self, referencing_path=None):
      
      if referencing_path is not None and self._spec_path == referencing_path:
        return self.relative_spec
      elif os.path.basename(self._spec_path) != self._target_name:
        return self.spec
      else:
        return self._spec_path
docs: How to reference this address in a BUILD file.
  
      :API: public