Creates a new MDI (Multiple Document Interface) object. Class specific
%OPTIONS are:
  -minsize => [X, Y]
    specifies the minimum size (width and height) in pixels;
    X and Y must be passed in an array reference
  -maxsize => [X, Y]
    specifies the maximum size (width and height) in pixels;
    X and Y must be passed in an array reference
  -minwidth  => N
  -minheight => N
  -maxwidht  => N
  -maxheight => N
    specify the minimum and maximum size width
    and height, in pixels
  -topmost => 0/1 (default 0)
    the window "stays on top" even when deactivated