A container form is smart-selector with a (possible) modal tab.
In it simplest form:
[ ] User finds a container by name or identifier in the autocomplete
[ ] Can use blue-pin to populate target container
[ ] Can use lock to lock container
Via a visual tab
[ ] User is presented an x,y,z visualization, very very simplified, of an existing container, and will click to place object
[ ] In visual mode user can select "fill down OR fill accross" and a temporary marker indicating where the object should be placed is auto-populated in the container.
Via a modal tab
[ ] Perhaps invoke a new container, or more complex visualization here
See also Container radial. To be used on Comprehensive, for example, but also for other forms whose objects can be contained.