private Selector replaceLeadingAppendersByEmptiness(Selector selector) {
while (!selector.isEmpty() && selector.getHead().isAppender()) {
selector.getHead().setParent(null);
selector.removeHead();
}
if (selector.isEmpty()) {
SimpleSelector empty = createEmptySimpleSelector(selector);
selector.addPart(empty);
}
return selector;
}
private Selector chopOffHead(Selector selector) {
if (!selector.isCombined()) return null;
selector.removeHead();
return selector;
}