Commentary enhancement in frame.el

* lisp/frame.el: Explain how to test whether a variable needs to
be added to the list of those which are watched for buffer
redisplay.

1 files changed, 7 insertions, 1 deletions

diff --git a/lisp/frame.el b/lisp/frame.el
index c629a9497c0..0e9f38589f9 100644
--- a/lisp/frame.el
+++ b/lisp/frame.el
@@ -2458,7 +2458,13 @@ See also `toggle-frame-maximized'."
 (make-obsolete-variable
  'window-system-version "it does not give useful information." "24.3")
 
-;; Variables which should trigger redisplay of the current buffer.
+;; Variables whose change of value should trigger redisplay of the
+;; current buffer.
+;; To test whether a given variable needs to be added to this list,
+;; write a simple interactive function that changes the variable's
+;; value and bind that function to a simple key, like F5.  If typing
+;; F5 then produces the correct effect, the variable doesn't need
+;; to be in this list; otherwise, it does.
 (mapc (lambda (var)
         (add-variable-watcher var (symbol-function 'set-buffer-redisplay)))
       '(line-spacing