anchor.diff:  import 'element.dart' as Our;
   import 'engine.dart';
   
  -
   _openNewScope(scope, k) {
  -
  -
     Map curr = {};
     curr.addAll(scope);
   
  
positive.code:     }
    }
  
  
    //Only resolve the prefix.
    //TODO handle library 'as ...' imports.
    visitPrefixedIdentifier(PrefixedIdentifier node) {
  
negative.code:   visitBlock(Block node) {
      _openNewScope(scope, (_) =>
          super.visitBlock(node));
    }
  
    visitFormalParameter(FormalParameter node) {
  