Add a doc string to display-time-string

* lisp/time.el: Add a doc string to `display-time-string',
because it's referred to in the manual, and is too mysterious
otherwise (bug#21002).

(cherry picked from commit 45559c584e5a4ddeed1539b028b50b95baa372f8)

diff --git a/lisp/time.el b/lisp/time.el
index e0d39b195869490b98984df9fe100be7e29e0290..ba5792441c4e617fe059f2a96031c23d31b241fc 100644 (file)
--- a/lisp/time.el
+++ b/lisp/time.el
@@ -108,7 +108,10 @@ A value of nil means 1 <= hh <= 12, and an AM/PM suffix is used."
   :type 'boolean
   :group 'display-time)
 
-(defvar display-time-string nil)
+(defvar display-time-string nil
+  "String used in mode lines to display a time string.
+It should not be set directly, but is instead updated by the
+`display-time' function.")
 ;;;###autoload(put 'display-time-string 'risky-local-variable t)
 
 (defcustom display-time-hook nil