anchor.diff:   * The value of the attribute to be treated as a string, equivalent
    * to `@` specification.
    */
  -@deprecated
   class NgAttr extends DirectiveAnnotation {
     final _mappingSpec = '@';
     const NgAttr(String attrName) : super(attrName);
  
positive.code:  * The value of the attribute to be treated as a two-way expression,
   * equivalent to `<=>` specification.
   */
  @deprecated
  class NgTwoWay extends DirectiveAnnotation {
    final _mappingSpec = '<=>';
    const NgTwoWay(String attrName) : super(attrName);
  
negative.code:  * The value of the attribute to be treated as a one time one-way expression,
   * equivalent to `=>!` specification.
   */
  class NgOneWayOneTime extends DirectiveAnnotation {
    final _mappingSpec = '=>!';
    const NgOneWayOneTime(String attrName) : super(attrName);
  