The items in a canvas are ordered for purposes of display,
with the first item in the display list being displayed
first, followed by the next item in the list, and so on.
Items later in the display list obscure those that are
earlier in the display list and are sometimes referred to
as being "on top" of earlier items.
When a new item is created it is placed at the end of the
display list, on top of everything else.
Widget commands may be used to re-arrange the order of the