code: function() {
            if(angular.isArray(selectedItemsList)) {
              var ixSmItem = selectedItemsList.indexOf(smItem);
              if(smItem[selectedAttribute]) {
                if(-1 === ixSmItem) {
                  selectedItemsList.push(smItem);
                }
              } else {
                if(-1 < ixSmItem) {
                  selectedItemsList.splice(ixSmItem, 1);
                }
              }
            }
          }
docs: Routine to keep the list of selected items up to date
  
  Adds/removes this item from `selectionModelSelectedItems`.