Which level do the beam hooks go in?

[rpatters1]

I have proposed #399 which would do away with the absurd duplication of beam levels, but unless (and until) that proposal is accepted I am trying to implement the spec as written. It is not clear to me which level the beam hooks should be on. My best guess is that they should be on the lowest level that does not have a beam hook. So, e.g., 32nd beam hooks would be attached to the 16th beam unless the 16th beam is broken (or it's a double dot or something). It would be nice to have this spelled out.