Replying to myself, since editing was getting out of control. A neat property of the 2nd approach is that if you ever reach a node R where R < S you're done: a

Replying to myself, since editing was getting out of control. A neat property of the 2nd approach is that if you ever reach a node R where R < S you're done: all children will be matched. A less neat property is that it won't allow multi-line matches, but I'm not sure those are allowed anyway.