code: def add_line_references(self, input_model):
          
          output_model = []
          for ln in input_model:
              line_len = len(ln[0])
              line_ref = ('// %4d' % ln[1]).rjust((self.max_line_len - line_len + 7), ' ')
              new_line = '%s %s\n' % (ln[0].rstrip(' \r\n\t\f'), line_ref)
              output_model.append([new_line, ln[1]])
          return output_model
docs: This function is a part of the model post-processing pipeline. For
          each line in the module, it adds a reference to the line number in
          the original draft/RFC from where the module line was extracted.
          :param input_model: The YANG model to be processed
          :return: Modified YANG model, where line numbers from the RFC/Draft
                   text file are added as comments at the end of each line in
                   the modified model