http://wiki.ecmascript.org/doku.php?id=harmony:rest_parameters The final parameter to a function is a rest parameter if it is prefixed by "...". FunctionExpression and FunctionDeclaration nodes have a new "rest" property that is null if there is no rest parameter, or contains an Identifer for the parameter. https://developer.mozilla.org/en-US/docs/SpiderMonkey/Parser_API#Functions Implemented by adding a new token, `_ellipsis`, which consists of three dots. Modified the body of parseFunction to allow a single rest parameter at the end of an argument list. Both the token and the rest parameter require `options.ecmaVersion` >= 6, otherwise three dots are tokenized as three dots.