The mxn multi widget does not show the level-window slider. This is because
# with multiple //topmost visible data nodes// it is not easy to decide which data node the level-window slider should manipulate
# with the PACS mode always active (BlackSwan context) the mouse can be used to change the level-window inside a render window
However, with T26490 and T26492 it is now required and possible to show the level-window slider and manipulate the //topmost visible data node// inside the currently active render window.