In principle a box.fixed container is a column container.
But a column container is always large enough to host its children.
A box.fixed container will have a horizontal and/or vertical scrollbar if its children occupy a space that is not fully enclosed by the box.fixed area.
There is a demo 3 Panels,images,download,dragNdrop at the menu option Help / sub-section Screen Object -Demos which uses a box.fixed container in the lower panel area.
See the following screenshot:
Functional specifications for box.fixed container related SOB commands:
Add – Container
SOB ( _
<Parent: number expression> ,_
"ADD" , _
"CONTAINER" , _
"BOX.FIXED" , _
<FIXED: integer expression> _