Confluence Cloud: What's the difference between "account-id" and "local-id" for mentioned users?

[Heinrich Ulbricht _WikiTraccs_]

When looking at the Confluence Cloud storage format for pages with @-mentions, I see this:

<ac:link>
   <ri:user ri:account-id="123456:abcb637e-7fae-4194-a2b6-dfabbb4c561d"
ri:local-id="ea4e6b2b-d6ff-4e7a-a860-fbba8f01d84e">
</ac:link>

I assume the account-id is the ID of the mentioned Atlassian account. But what is the local-id value? This seems to be a new addition.