for removed_root_id in removed:
model = dict(combined_references[removed_root_id])
del model["attributes"]
events.append({ "kind" : "RootRemoved",
"model" : model })
for added_root_id in added:
Document._value_record_references(combined_references,
combined_references[added_root_id],
value_refs)
model = dict(combined_references[added_root_id])
del model["attributes"]
events.append({ "kind" : "RootAdded",
"model" : model })
for id in to_references:
if id in from_references: