A DAGMC-based analysis allows a number of attributes of the geometry
to be defined within the geometry file. These characteristics
generally relate to the physical behavior of the volume, for example
its material definition or boundary conditions.

Before the discussion of specific attributes, the practice of
"grouping" needs to be explained. A group is essentially a collection
of volumes or surfaces that share a common attribute; the practical
usage of "grouping" will be explained in the next section.

The general format for creating/adding volumes to a group is:
::

    CUBIT> group "group.name" add vol/surf ...

For example, to create a group called "moderator" containing volumes
5, 6, 7, and 10, the following command would be used:
::

    CUBIT> group "moderator" add vol 5 to 8 10

Another example, shows that groups don't have to just contain
volumes, but can contain surfaces too. Below the group
"shield.boundary" is created with surfaces 16 and 37:
::

    CUBIT> group "shield.boundary" add surf 16 37

Due to the importance of using the ``group`` command reading the CUBIT
manual section on its full usage is highly recommended.
