Related smells: Unstable Interface, Incomplete Library Class
Spillover happens when some symbols that should have been a part of the nonterminal definition, are not included in its right hand side, and appended every time to its use. This creates a co-change relationship between the nonterminal and the context of its use. If every time a definition of a nonterminal is changed in a particular way, all occurrences of the same nonterminal needs to be updated, this smell is detected.