This widget simply draws its box, and possibly it's label. Putting it
before some other widgets and making it big enough to surround them
will let you draw a frame around them.
The first constructor sets box() to FL_NO_BOX, which
means it is invisible. However such widgets are useful as placeholders
values. To change the box to something visible, use box(n).
The second form of the constructor sets the box to the specified box
The destructor removes the box.