public XPathMatcher activateField(Field field, int initialDepth) {
ValueStore valueStore =
fValueStoreCache.getValueStoreFor(field.getIdentityConstraint(), initialDepth);
XPathMatcher matcher = field.createMatcher(valueStore);
fMatcherStack.addMatcher(matcher);
matcher.startDocumentFragment();
return matcher;
} // activateField(Field):XPathMatcher
/**
* Ends the value scope for the specified identity constraint.