Create a compound alternative group selection
create_compound_group_selection.RdBuild a CompoundGroupSelection entry, used inside a
CompoundProperties to record which alternative is selected within an
alternative group. Internal machinery only: the friendly alternatives
selection in add_simulation()'s compounds argument is the
user-facing way to select an alternative; this constructor and the
COMPOUND_* group constants it takes are not part of the public API.
Value
A CompoundGroupSelection object.