const typename Model::Node& el, const AttributeSignature& signature) const
const typename Model::Element& el, const AttributeSignature& signature) const
  refineAttribute(const SmartPtr<Element>& elem,		  const typename Model::Node& el, const AttributeSignature& signature) const  {    if (SmartPtr<Attribute> attr = getAttribute(el, signature)) elem->setAttribute(attr);    else elem->removeAttribute(signature);  }