Subsequences (often called groups) may be used to avoid Misformat, but really hamper the understanding of the system if used excessively. This smell often correlates with production rules being TooRamose.
Related smells: TooRecursive Misformat
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.