The ccm select -show -stack command pops
the selection set stack, setting the current selection set to the
symmetric difference between its previous objects and the popped selection
set. That is, the new selection set contains objects that were in
either the previous selection set, or in the popped selection set,
but not both. For example, if the top of the stack contains objects
{a,b,c} and the current selection set contains {b,c,d}, the current
selection set after the command is {d,a}.
About this task
ccm select -symdiff