boolean scanPrevious = false;
for (; index > -1; index--) {
Expression child = collectionExpression.getChild(index);
String text = child.toParsedText();
// Handle 'NOT'
if (text.equalsIgnoreCase(NOT) || isNotExpression(child)) {
// Two consecutive 'NOT' or 'IS' is invalid or 'NOT IS' is not valid