internal void TestDrop(IDockDragSource dragSource, DockOutlineBase dockOutline) { if (VisibleNestedPanes.Count == 1) { DockPane pane = VisibleNestedPanes[0]; if (!dragSource.CanDockTo(pane)) { return; } Point ptMouse = Control.MousePosition; uint lParam = Win32Helper.MakeLong(ptMouse.X, ptMouse.Y); if (NativeMethods.SendMessage(Handle, (int)Win32.Msgs.WM_NCHITTEST, 0, lParam) == (uint)Win32.HitTest.HTCAPTION) { dockOutline.Show(VisibleNestedPanes[0], -1); } } }