code: public Boolean onClick(AppCompatActivity act, IItem item) {
          //if we are current in CAB mode, and we remove the last selection, we want to finish the actionMode
          if (mActionMode != null && (mSelectExtension.getSelectedItems().size() == 1) && item.isSelected()) {
              mActionMode.finish();
              mSelectExtension.deselect();
              return true;
          }
  
          if (mActionMode != null) {
              // calculate the selection count for the action mode
              // because current selection is not reflecting the future state yet!
              int selected = mSelectExtension.getSelectedItems().size();
              if (item.isSelected())
                  selected--;
              else if (item.isSelectable())
                  selected++;
              checkActionMode(act, selected);
          }
  
          return null;
      }
docs: implements the basic behavior of a CAB and multi select behavior,
  including logics if the clicked item is collapsible
  
  @param act  the current Activity
  @param item the current item
  @return null if nothing was done, or a boolean to inform if the event was consumed