// create a new attribute each time, by demand
// supporting of old attributes is too slow (synch each time) and buggy on redo
// (if attribute is deleted and created, the abort updates attriute and makes the Attr invalid)
// create a new attribute each time, by demand
// supporting of old attributes is too slow (synch each time) and buggy on redo
// (if attribute is deleted and created, the abort updates attriute and makes the Attr invalid)