(debug-on-entry): Fix docstring.

1 files changed, 9 insertions, 3 deletions

diff --git a/lisp/emacs-lisp/debug.el b/lisp/emacs-lisp/debug.el
index 0745508b64b..0ee67355bf4 100644
--- a/lisp/emacs-lisp/debug.el
+++ b/lisp/emacs-lisp/debug.el
@@ -656,10 +656,16 @@ functions to break on entry."
 ;;;###autoload
 (defun debug-on-entry (function)
   "Request FUNCTION to invoke debugger each time it is called.
+
 When called interactively, prompt for FUNCTION in the minibuffer.
-If you tell the debugger to continue, FUNCTION's execution proceeds.
-This works by modifying the definition of FUNCTION,
-which must be written in Lisp, not predefined.
+
+This works by modifying the definition of FUNCTION.  If you tell the
+debugger to continue, FUNCTION's execution proceeds.  If FUNCTION is a
+normal function or a macro written in Lisp, you can also step through
+its execution.  FUNCTION can also be a primitive that is not a special
+form, in which case stepping is not possible.  Break-on-entry for
+primitive functions only works when that function is called from Lisp.
+
 Use \\[cancel-debug-on-entry] to cancel the effect of this command.
 Redefining FUNCTION also cancels it."
   (interactive "aDebug on entry (to function): ")