Anonymous alternative syntax help !

[ghost]

grammar
match {
    r#"[^"]"# => "StringLiteral_0",
    r#"(\\\\|\\'|\\"|\\`|\\t|\\b|\\n|\\r|\\f|\\u[0-9A-F]{4}|\\U[0-9A-F]{6})"# => "ESCAPED_CHARACTER",
} else {

}

Test = ("StringLiteral_0", "ESCAPED_CHARACTER")* // zero or more StringLiteral_0 or ESCAPED_CHARACTER

I want to a anonymous alternative syntax to represent some rule in ad-hoc mode. Is there any workaround rather than define a named nonterminal.