code: def _add_default_source(self):
          
          if self.modname:
              if self._package_path:
                  filename = os.path.join(self._package_path, DEFAULT_FILENAME)
                  if os.path.isfile(filename):
                      self.add(ConfigSource(load_yaml(filename), filename, True))
docs: Add the package's default configuration settings. This looks
          for a YAML file located inside the package for the module
          `modname` if it was given.