anchor.diff:   */
   abstract class TypeAnnotation extends AstNode {
     /**
  +   * The question mark indicating that the type is nullable, or `null` if there
  +   * is no question mark.
  +   */
  +  Token get question;
  +
  +  /**
      * Return the type being named, or `null` if the AST structure has not been
      * resolved.
      */
  
positive.code:   void set name(Identifier identifier);
  
    /**
     * The question mark indicating that the type is nullable, or `null` if there
     * is no question mark.
     */
    Token get question;
  
    /**
     * Set the question mark indicating that the type is nullable to the given
     * [token].
     */
  
negative.code:    * [parameters].
     */
    void set parameters(FormalParameterList parameters);
  
    /**
     * Set the question mark indicating that the type is nullable to the given
  