* lisp/subr.el (sit-for): Add comment with a short history.

diff --git a/lisp/subr.el b/lisp/subr.el
index 0a95cebd1a66eac45428e4eb63ac902fc3bc9cb0..4fba469868f88b0860db4703a470f00ef7e741a2 100644 (file)
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2151,6 +2151,10 @@ where the optional arg MILLISECONDS specifies an additional wait period,
 in milliseconds; this was useful when Emacs was built without
 floating point support."
   (declare (advertised-calling-convention (seconds &optional nodisp) "22.1"))
+  ;; This used to be implemented in C until the following discussion:
+  ;; http://lists.gnu.org/archive/html/emacs-devel/2006-07/msg00401.html
+  ;; Then it was moved to C using an implementation based on an idle timer,
+  ;; which was then replaced by the use of read-event.
   (if (numberp nodisp)
       (setq seconds (+ seconds (* 1e-3 nodisp))
             nodisp obsolete)