Consider adding a dummy lowercase, unexported method to the Rope interface

Consider adding an unexported method to the Rope interface such as

private()

This way clients of your Rope package can't easily write their own implementation of Rope. It also warns clients that they shouldn't try to implement Rope. You want to do this for two reasons:

1. The Rope functions will either panic or not perform as intended if handed a custom implementation of Rope
2. Knowing that others haven't implemented the Rope interface means that you can safely add new methods to Rope as your package evolves.