Exotic

This smell is in contradiction with Underuse, and states that using notational features that are uncommon, obscure or overly exotic, should be limited. Excessive use of features idiosyncratic for one particular notation, will result in a vendor lock-in. For example, if a notation allows context handling (pushing the grammar outside the comfort zone of CFGs), using it is only fully justified when the result is too cumbersome otherwise.

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.