Uszkoreit, H., & Peters, S. (1986). On some formal properties of metarules. In The Formal Complexity of Natural Language (pp. 227-250). Springer, Dordrecht.
Grammars contain rules for generating sentences. Metarules are statements about these rules. They are metagrammatical devices that can be used to generate rules of the grammar or to encode certain relations among them such as redundancies in their form.
The linguistic framework of Generalized Phrase, Structure, Grammar (GPSG) utilizes meta-rules in describing natural languages. The rules of a GPSG are context-free phrase-structure rules. A metarule is an ordered pair of rule templates that is to be interpreted as follows: if the grammar contains a rule of the form, A, it also contains a corresponding rule of the form B. As this interpretation suggests, the set of grammar rules is closed under application of the metarules. It is therefore possible to give an inductive definition of the grammar by listing just a subset of the rules – called the basic rules – together with the list of metarules; the full set of rules is derived by applying the metarules to the basic rules and then, recursively, to the output of all such applications.