syntax VoidRule = RuleAttributes "void" Name "=" RuleExpression SimpleRuleBody;

Its main purpose is to describe the rules that recognize minor grammar entities, such as space characters (whitespace, tab, end-of-line) and comments.

Since Nitra automatically inserts whitespaces by default, the two void rules – s and S – are usually required. The s rule should recognize minor characters (space and comments). The S rule should be similar to s and in addition it should contain a predicate that verifies that incoming flow of characters doesn’t contain the characters identical to identifier characters of the processed language.

S is placed after a keyword described with literals locally in the grammar.

void S = !IdentifierPartCharacters s;
void s = IgnoreToken*;

See also

RuleAttributes
Name
RuleExpression
SimpleRuleBody