Implementation notes on react's scheduling model as of (shortly before) 16.8.0
While the public API intended for users to use is the
scheduler package, the reconciler currently
does not use
scheduler's priority classes internally.
ReactFiberScheduler has its own internal "mini-scheduler" that uses the
indirectly for its deadline-capable scheduleCallback.
This is kind of a documentation of implementation details that I suppose will be gone by the end of the year, but what can you do.