This article is pretty frustrating as it doesn't introduce rowan or green trees and I had to read a bit to know you were even talking about a rust lib. Beyond that I don't know if I ever encountered a modern syntax tree lib that didn't have at least a pointer to the beginning and end of the token lexed at the leaf node level. If you don't have this error reporting becomes either awkward or complicated for the developer or the end user.
This article is pretty frustrating as it doesn't introduce rowan or green trees and I had to read a bit to know you were even talking about a rust lib. Beyond that I don't know if I ever encountered a modern syntax tree lib that didn't have at least a pointer to the beginning and end of the token lexed at the leaf node level. If you don't have this error reporting becomes either awkward or complicated for the developer or the end user.