...
- Check and Improve error handling
- Re-use CpsPath Exception (wrap IllegalState exception)
- Clean up, simplify rules and remove redundant legacy limitations
- Better names (check name-casing conventions Antrl)
- Consider using predefined xpath grammer: https://github.com/antlr/grammars-v4/tree/master/xpath/xpath31
- Even just study it or extract small parts to get correct definition of valid container-names etc.