master 935f400a33: Clarify cl-incf/decf doc strings

[Lars Ingebrigtsen]

branch: master
commit 935f400a33d6ff0f5d61fc7ade688a4378613882
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>

    Clarify cl-incf/decf doc strings
    
    * lisp/emacs-lisp/cl-lib.el (cl-incf):
    (cl-decf): Clarify that nil isn't a valid value for X (bug#31715).
---
 lisp/emacs-lisp/cl-lib.el | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lisp/emacs-lisp/cl-lib.el b/lisp/emacs-lisp/cl-lib.el
index 4e60a3c63d..3f40ab0760 100644
--- a/lisp/emacs-lisp/cl-lib.el
+++ b/lisp/emacs-lisp/cl-lib.el
@@ -114,7 +114,10 @@ a future Emacs interpreter will be able to use it.")
 (defmacro cl-incf (place &optional x)
   "Increment PLACE by X (1 by default).
 PLACE may be a symbol, or any generalized variable allowed by `setf'.
-The return value is the incremented value of PLACE."
+The return value is the incremented value of PLACE.
+
+If X is specified, it should be an expression that should
+evaluate to a number."
   (declare (debug (place &optional form)))
   (if (symbolp place)
       (list 'setq place (if x (list '+ place x) (list '1+ place)))
@@ -123,7 +126,10 @@ The return value is the incremented value of PLACE."
 (defmacro cl-decf (place &optional x)
   "Decrement PLACE by X (1 by default).
 PLACE may be a symbol, or any generalized variable allowed by `setf'.
-The return value is the decremented value of PLACE."
+The return value is the decremented value of PLACE.
+
+If X is specified, it should be an expression that should
+evaluate to a number."
   (declare (debug cl-incf))
   (if (symbolp place)
       (list 'setq place (if x (list '- place x) (list '1- place)))