Improve documentation of hooks related to saving buffers

* lisp/files.el (write-file-functions, write-contents-functions)
(before-save-hook, after-save-hook): Note that these are only used
by save-buffer.

* doc/lispref/backups.texi (Auto-Saving):
* doc/lispref/files.texi (Saving Buffers): Mention that
save-related hooks are not run by auto-saving.  (Bug#25460)

2 files changed, 10 insertions, 1 deletions

diff --git a/doc/lispref/backups.texi b/doc/lispref/backups.texi
index 83d826018ca..361fa81099b 100644
--- a/doc/lispref/backups.texi
+++ b/doc/lispref/backups.texi
@@ -545,6 +545,11 @@ effect in an existing buffer until the next time auto-save mode is
 reenabled in it.  If auto-save mode is already enabled, auto-saves
 continue to go in the same file name until @code{auto-save-mode} is
 called again.
+
+Note that setting this variable to a non-@code{nil} value does not
+change the fact that auto-saving is different from saving the buffer;
+e.g., the hooks described in @ref{Saving Buffers} are @emph{not} run
+when a buffer is auto-saved.
 @end defopt
 
 @defun recent-auto-save-p
diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 6f015e2d643..49cb150dc64 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -403,7 +403,11 @@ buffer name instead.
 @end deffn
 
   Saving a buffer runs several hooks.  It also performs format
-conversion (@pxref{Format Conversion}).
+conversion (@pxref{Format Conversion}).  Note that these hooks,
+described below, are only run by @code{save-buffer}, they are not run
+by other primitives and functions that write buffer text to files, and
+in particular auto-saving (@pxref{Auto-Saving}) doesn't run these
+hooks.
 
 @defvar write-file-functions
 The value of this variable is a list of functions to be called before