Before, there might have been one predicate that, to get an urgency of 10,
you'd have to pass an N of 0.01, and another that to get an urgency of 10
you'd have to pass an N of 20.  Now, N's of the same order of magnitude
produce changes of the same order of magnitude.

Turns out headings always have a 'priority property, so we don't need to have
our own fallback.  Org will provide.