How do i include message fields in the Alert Action Message for Per document monitor

How can I access log data in alert message for Per document monitor?
In the documentation I was able to find only one example of such monitor and its message included only reference to finding and document.
I’d like to add some document fields jut like Per query monitor allows via ctx.results.0.hits.hits.
I cannot use Per query monitor since I’m interested in action per alert, not per execution at the same time Per document monitor doesn’t seem to include ctx.results.0.hits.hits. Also I don’t know how can I introspect structure of context available, I tried to run Per document monitor _execute via DevTools, but it doesn’t match the ctx structure (e.g. there were no ctx.alerts.0.related_doc_ids path, although the data was present just under different path) and _execute result also doesn’t seem to include any document data similar to how it is done for _execute of Per query monitor ctx.results.0.hits.hits - nor path nor data.