For convenience, set can also be written as a nonterminal, in which case it represents the set of all terminals to which that nonterminal could expand. Line break constraints are only present in the syntactic grammar . Many rules in the grammars occur in groups of analogous rules. If these arguments later parametrize the nonterminal on the left side of a rule, that rule is implicitly replicated into a set of rules in each of which a grammar argument is consistently substituted by one of its variants. A few lexical rules have too many expansions to be practically listed.
Some lexical rules contain the metaword except .
These rules match any expansion that is listed before the except but that does not match any expansion after the except . All of these rules ultimately expand into single characters.