* lispref/lists.texi (List Elements): Undocument nth, nthcdr with n < 0

doc/lispref/ChangeLog

@@ -1,3 +1,8 @@
+2013-08-13  Glenn Morris  <rgm@gnu.org>
+
+	* lists.texi (List Elements):
+	Undocument behavior of nth and nthcdr with n < 0.  (Bug#15059)
+
 2013-08-13  Xue Fuqiao  <xfq.free@gmail.com>
 
 	* frames.texi (Display Feature Testing): Add indexes.

doc/lispref/lists.texi

@@ -270,8 +270,10 @@ are numbered starting with zero, so the @sc{car} of @var{list} is
 element number zero.  If the length of @var{list} is @var{n} or less,
 the value is @code{nil}.
 
-If @var{n} is negative, @code{nth} returns the first element of
-@var{list}.
+@c Behavior for -ve n undefined since 2013/08; see bug#15059.
+@ignore
+If @var{n} is negative, @code{nth} returns the first element of @var{list}.
+@end ignore
 
 @example
 @group
@@ -281,10 +283,6 @@ If @var{n} is negative, @code{nth} returns the first element of
 @group
 (nth 10 '(1 2 3 4))
      @result{} nil
-@end group
-@group
-(nth -3 '(1 2 3 4))
-     @result{} 1
 
 (nth n x) @equiv{} (car (nthcdr n x))
 @end group
@@ -300,7 +298,8 @@ This function returns the @var{n}th @sc{cdr} of @var{list}.  In other
 words, it skips past the first @var{n} links of @var{list} and returns
 what follows.
 
-If @var{n} is zero or negative, @code{nthcdr} returns all of
+@c "or negative" removed 2013/08; see bug#15059.
+If @var{n} is zero, @code{nthcdr} returns all of
 @var{list}.  If the length of @var{list} is @var{n} or less,
 @code{nthcdr} returns @code{nil}.
 
@@ -314,7 +313,7 @@ If @var{n} is zero or negative, @code{nthcdr} returns all of
      @result{} nil
 @end group
 @group
-(nthcdr -3 '(1 2 3 4))
+(nthcdr 0 '(1 2 3 4))
      @result{} (1 2 3 4)
 @end group
 @end example