*/
    public XPathMatcher activateField(Field field, int initialDepth) {
        ValueStore valueStore =
            fValueStoreCache.getValueStoreFor(field.getIdentityConstraint(), initialDepth);
        setMayMatch(field, Boolean.TRUE);
        XPathMatcher matcher = field.createMatcher(this, valueStore);
        fMatcherStack.addMatcher(matcher);
        matcher.startDocumentFragment();
        return matcher;
    }