code: def add_highlight(self, hl_group, line, col_start=0,
                        col_end=-1, src_id=-1, async_=None,
                        **kwargs):
          
          async_ = check_async(async_, kwargs, src_id != 0)
          return self.request('nvim_buf_add_highlight', src_id, hl_group,
                              line, col_start, col_end, async_=async_)
docs: Add a highlight to the buffer.