Improve DND documentation

* doc/lispref/frames.texi (Drag and Drop):
* src/xfns.c (Fx_begin_drag): Document that x-begin-drag may
return immediately if no mouse buttons are held down.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/xfns.c b/src/xfns.c
index 47321a1d6b2..4b5d30bca25 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -6827,7 +6827,12 @@ instead.
 
 If ALLOW-CURRENT-FRAME is not specified or nil, then the drop target
 is allowed to be FRAME.  Otherwise, no action will be taken if the
-mouse buttons are released on top of FRAME.  */)
+mouse buttons are released on top of FRAME.
+
+This function will sometimes return immediately if no mouse buttons
+are currently held down, and should only be called in situations where
+it is known that some are being held down down, such as immediately
+after a `down-mouse-1' event.  */)
   (Lisp_Object targets, Lisp_Object action, Lisp_Object frame,
    Lisp_Object return_frame, Lisp_Object allow_current_frame)
 {