Fix outdated timestamp documentation in Elisp manual.

* doc/lispref/files.texi (File Attributes):
* doc/lispref/text.texi (Undo):
Time stamp resolution is now 1 picosecond, not 1 second.
* etc/NEWS: Document increased precision in undo list.

Fixes: debbugs:12706

3 files changed, 14 insertions, 7 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 6bd0297252d..a767bbf1fce 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,10 @@
+2012-10-23  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Fix outdated timestamp documentation in Elisp manual (bug#12706).
+        * files.texi (File Attributes):
+        * text.texi (Undo):
+        Time stamp resolution is now 1 picosecond, not 1 second.
+
 2012-10-23  Chong Yidong  <cyd@gnu.org>
 
         * display.texi (Font Lookup): Remove font-list-limit.
diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 9424a661236..285e6406426 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -1220,9 +1220,8 @@ point number.
 The file's @acronym{GID}, likewise.
 
 @item
-The time of last access, as a list of two integers.
-The first integer has the high-order 16 bits of time,
-the second has the low 16 bits.  (This is similar to the
+The time of last access, as a list of four integers @code{(@var{sec-high}
+@var{sec-low} @var{microsec} @var{picosec})}.  (This is similar to the
 value of @code{current-time}; see @ref{Time of Day}.)  Note that on
 some FAT-based filesystems, only the date of last access is recorded,
 so this time will always hold the midnight of the day of last access.
diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index a5910ea921b..50b97cd4204 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -1233,11 +1233,12 @@ reinsert it is @code{(abs @var{position})}.  If @var{position} is
 positive, point was at the beginning of the deleted text, otherwise it
 was at the end.
 
-@item (t @var{high} . @var{low})
+@item (t @var{sec-high} @var{sec-low} @var{microsec} @var{picosec})
 This kind of element indicates that an unmodified buffer became
-modified.  The elements @var{high} and @var{low} are two integers, each
-recording 16 bits of the visited file's modification time as of when it
-was previously visited or saved.  @code{primitive-undo} uses those
+modified.  The list @code{(@var{sec-high} @var{sec-low} @var{microsec}
+@var{picosec})} represents the visited file's modification time as of
+when it was previously visited or saved, using the same format as
+@code{current-time}; see @ref{Time of Day}.  @code{primitive-undo} uses those
 values to determine whether to mark the buffer as unmodified once again;
 it does so only if the file's modification time matches those numbers.