Determines which objects are selected and gripped
(ssgetfirst)
Returns a list of two selection sets similar to those passed to sssetfirst. The first element in the list is a selection set of entities that are gripped but not selected. The second element is a selection set of entities that are both gripped and selected. Either (or both) elements of the list can be nil.
So, (setq ss (cadr (ssgetfirst))) will give you the ss of the currently selected items.
HTH, Jeff