ASTs

RustPython

Successfully parses invalid programs
synthesises missing nodes (var a = crates an empty identifier for the initializer)
Gives access to leading/trailing node trivia → AST design influences the granularity at which trivia can be queried. There seems to be no way to query trivia in the middle of a node
It seems that TypeScript creates an emit node in refactors that differs from a parsed node (e.g. comments are stored on the node)
Stores (byte) ranges on the node