syntax ExtensionRule = "|" RuleAttributes (Name "=")? RuleExpression Precedence? ExtensionRuleBody?;

ExtensionRule lets you specify a number of extensions either directly in the extensible rule, or using ExtendSyntax.

For example:

| Object = "{" (Property; ",")* "}";

See also

ExtendSyntax
ExtensionRule
RuleAttributes
Name
RuleExpression
Precedence
ExtensionRuleBody