code: def check(self, diff):
          
          relative_path = relative_to_contrib(diff, self.project)
          subpackage_name = relative_path.parts[0]
          assert re_test(SUBPACKAGE_NAME_REGEX, subpackage_name)
docs: Check that the name of the subpackage within contrib is valid
  
          The package name must match ``user_[a-zA-Z0-9_]+``.