validateNewPropertyName(propertyName);
// Locate the existing one.
PropertyModel existing = get(existingPropertyName);
// Use the case normalized property name.
int pos = _propertyNames.indexOf(existing.getPropertyName());
PropertyModel newModel = new PropertyModelImpl(this, propertyName, conduit, _messages);
_properties.put(propertyName, newModel);
int offset = position == RelativePosition.AFTER ? 1 : 0;