Getting number of strokes in tremolo?

Does anyone know of a way of getting the number of strokes in a Tremolo element?

I've experimented with the following properties:
1) userName — returns 'Tremolos' (irrespective of number of strokes)
2) symbol — returns undefined
3) name — returns 'Tremolo'
4) subtype — returns undefined

The only thing that I can see that changes depending on the number of strokes is the bbox.height value, but that seems like a very hacky way to work out the number of strokes!