Depends on D19120. Ref T13083. When you write a fact engine, it's currently somewhat difficult to figure out exactly what it's doing. It would also be difficult to diagnose bugs or report them to the upstream.
To ease this, add a page which shows all the facts an object generates. This allows you to iterate on an engine quickly without needing to reanalyze facts, take a screenshot, easily compare the timeline to the fact view, etc.