1 files changed, 3 insertions, 0 deletions

diff --git a/src/buffer.h b/src/buffer.h
index 1fb322e3ed9..397b97579e6 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -584,6 +584,9 @@ struct buffer
   /* This isn't really used by the C code, so could be deleted.  */
   Lisp_Object backed_up;
   /* Length of file when last read or saved.
+     -1 means auto saving turned off because buffer shrank a lot.
+     -2 means don't turn off auto saving if buffer shrinks.
+       (That value is used with buffer-swap-text.)
      This is not in the  struct buffer_text
      because it's not used in indirect buffers at all.  */
   Lisp_Object save_length;