For each node that has an attr of key ‘handle’:

1. generates a unique id attr added to the node, if not already present

2. parses each ‘handle’ attr value in the form

handle=handle_name [handle_value]

where the handle_value string is an optional string separated from handle_name that may or may not be present, and replaces this key-value pair with

handle=handle_name|handle_value|id

while using the empty string for ‘handle_value’, if not present