anchor.diff:  class BlockScope extends EnclosedScope {
     /**
      * Initialize a newly created scope, enclosed within the [enclosingScope],
  -   * based on the given [classElement].
  +   * based on the given [block].
      */
     BlockScope(Scope enclosingScope, Block block) : super(enclosingScope) {
       if (block == null) {
  
positive.code: 
    /**
     * Add the given [element] to this scope. If there is already an element with
     * the given name defined in this scope, then an error will be generated and
     * the original element will continue to be mapped to the name. If there is an
     * element with the given name in an enclosing scope, then a warning will be
     * generated but the given element will hide the inherited element.
     */
    void define(Element element) {
      String name = _getName(element);
  
negative.code: 
    /**
     * Initialize a newly created scope representing the names imported into the
     * [_definingLibrary].
     */
    LibraryImportScope(this._definingLibrary) {
      _createImportedNamespaces();
  