The purpose of a structure editor is to make editing a syntax tree as quick and painless as possible. There are three ways to build a structure editor:

1. By appending "with seditable" at the end of a type
2. By specifying a context free grammar which can contain types declared with the first method
   
3. By subclassing the node class
   

A highly efficient and responsive backend has been developed to support large syntax trees. A full programming language, Eastwest, has been built with OSET.

I suggest getting it and then following the manual.

OSET in action: