What is the role of Binary?

[Xazax-hun]

After 802c786, Handler is no longer Binary, but its interface still has only two getters. We had some code that relied on some nodes being Binary so we can reduce the amount of code we need to write by utilizing the more regular structure of IPR. Does this mean we should no longer rely on nodes being Binary or Unary but call the specific getters directly? (Instead of using first/second in generic code.)