diff --git a/docs/dnd-protocol.rst b/docs/dnd-protocol.rst
index b3cd0846e..230beab9a 100644
--- a/docs/dnd-protocol.rst
+++ b/docs/dnd-protocol.rst
@@ -60,11 +60,13 @@ to inform the terminal that it no longer wants drops.
 Whenever the user drags something over the window, the terminal will send an
 escape code of the form::
 
-    OSC _dnd_code ; t=m:x=x:y=y:X=X:Y=Y ; optional MIME list ST
+    OSC _dnd_code ; t=m:x=x:y=y:X=X:Y=Y:o=O ; optional MIME list ST
 
 Here, ``x, y`` identify the cell over which the drag is currently present.
 The ``(0, 0)`` cell is at top left of the screen. ``X and Y`` are the pixel
-offsets from the top-left. The optional list of MIMES is a space separated
+offsets from the top-left. The ``O`` value is the set of allowed operations,
+which can be ``1`` for copy, ``2`` for move and ``3`` for either, at the
+client's discretion. The optional list of MIMES is a space separated
 list of MIME types that are available for dropping. To avoid overhead, the
 terminal should only send this list for the first move event and subsequently
 only if the list changes.