HWND jump_if_window [jump_if_not_window]
If HWND is a window, Gotos jump_if_window, otherwise, Gotos jump_if_not_window (if specified).
GetDlgItem $0 $HWNDPARENT 1 IsWindow $0 0 +3 MessageBox MB_OK "found a window" Goto +2 MessageBox MB_OK "no window"
Command introduced with NSIS v1.51
