protected void processListItem(String listItem) {
// check what type of a value the list item is.
// Each item in the list must be an individual attribute value or a range.
// List items can not themselves be lists, wild-cards, or increments.
ScheduleExpressionType listItemType = ScheduleExpressionTypeUtil.getType(listItem);
switch (listItemType) {
case SINGLE_VALUE:
SingleValue singleVal = new SingleValue(listItem);
this.processSingleValue(singleVal);
return;