anchor.diff:   *
    *     class NumberListParser2 extends NumberListGrammar2 {
    *       void initialize() {
  - *         action('element', (value) => int.parse(value));
  + *         element((value) => int.parse(value));
    *       }
    *     }
    *
  
positive.code:  * Experimental helper to compose complex grammars from various primitive
   * parsers using variable references.
   *
   * The difference of this implementation and [CompositeParser] is that
   * subclasses can define and refer to productions using variables. The
   * accessors themselves are not actually implement anywhere, but their
   * behavior is defined in [noSuchMethod] and mapped a collection using
   * the behavior defined in the superclass.
   *
   * Consider the following example to parse a list of numbers:
   *
  
negative.code:  * as all productions are undefined from the perspective of the analyzer. Pay
   * attention with production names that conflict with methods defined in the
   * superclasses. The generated JavaScript code is noticably bigger, due to the
   * use of [noSuchMethod]. The resulting parsers identical and parse-speed is
   * the same, onlyt he construction of the parser itself is slightly more
   * expensive.
   */
  class CompositeParser2 extends CompositeParser {
  
  