Adds or removes graphics from an existing group of objects. Allows you to add on
to an existing Wall or Slab in the 3D environment. When you activate the Add to or
remove graphics from a Group command, the Add to or remove graphics from a Group ribbon
is displayed so that you can create or remove objects from the existing structure.
The Add to or remove graphics from a Group command is active only when you select
a Wall or Slab to modify.