* buffers.texi (Swapping Text): Recommend setting

write-region-annotate-functions and buffer-saved-size.

* backups.texi (Auto-Saving): Document buffer-saved-size = -2.

doc/lispref/ChangeLog

+2009-07-16  Richard Stallman  <rms@gnu.org>
+
+	* buffers.texi (Swapping Text): Recommend setting
+	write-region-annotate-functions and buffer-saved-size.
+
+	* backups.texi (Auto-Saving): Document buffer-saved-size = -2.
+
 2009-07-15  Glenn Morris  <rgm@gnu.org>
 
 	* edebug.texi: Minor re-phrasings throughout.

doc/lispref/backups.texi

@@ -632,6 +632,10 @@ this buffer due to a substantial decrease in size.  Explicitly saving
 the buffer stores a positive value in this variable, thus reenabling
 auto-saving.  Turning auto-save mode off or on also updates this
 variable, so that the substantial decrease in size is forgotten.
+
+If it is @minus{}2, that means this buffer should disregard changes in
+buffer size; in particular, it should not shut off auto-saving
+temporarily due to changes in buffer size.
 @end defvar
 
 @defvar auto-save-list-file-name

doc/lispref/buffers.texi

@@ -1192,6 +1192,13 @@ overlays, the text properties, the undo list, the value of the
 enable-multibyte-characters}), etc.
 @end defun
 
+  If you use @code{buffer-swap-text} on a file-visiting buffer, you
+should set up a hook to save the buffer's original text rather than
+what it was swapped with.  @code{write-region-annotate-functions}
+works for this purpose.  You should probably set
+@code{buffer-saved-size} to @minus{}2 in the buffer, so that changes
+in the text it is swapped with will not interfere with auto-saving.
+
 @node Buffer Gap
 @section The Buffer Gap