Add more spec comments

v2/claim.go

@@ -196,9 +196,14 @@ func (claim *Claim) HandleSelectionClear (
 	connection *xgbutil.XUtil,
 	event xevent.SelectionClearEvent,
 ) {
-	// If a client gives up ownership of a selection or if some other client
-	// executes a SetSelectionOwner for it and thus reassigns it forcibly,
-	// the previous owner will receive a SelectionClear event.
+	// When some other client acquires a selection, the previous owner
+	// receives a SelectionClear event. The timestamp argument is the time
+	// at which the ownership changed hands, and the owner argument is the
+	// window the previous owner specified in its SetSelectionOwner request.
+	// If an owner loses ownership while it has a transfer in progress (that
+	// is, before it receives notification that the requestor has received
+	// all the data), it must continue to service the ongoing transfer until
+	// it is complete.
 	claim.active = false
 }