Superset

Some grammars represent a superset of the intended language. This may become a problem if the parser based on the grammar is to be used as a correctness oracle, since in this role it is inadequate.

Reference

Mats Stijlaart and Vadim Zaytsev. 2017. Towards a taxonomy of grammar smells. In Proceedings of the 10th ACM SIGPLAN International Conference on Software Language Engineering (SLE 2017). ACM, New York, NY, USA, 43-54.