anchor.diff:        var type = data['type'];
   
         if (type == 'sourceCode') {
  -        var sourceCode = data['sourceCode'];
  -        userCodeEditor.document.value = sourceCode['main.dart'] ?? '';
  -        solutionEditor.document.value = sourceCode['solution.dart'] ?? '';
  -        testEditor.document.value = sourceCode['test.dart'] ?? '';
  -        htmlEditor.document.value = sourceCode['index.html'] ?? '';
  -        cssEditor.document.value = sourceCode['styles.css'] ?? '';
  +        setContextSources(Map<String, String>.from(data['sourceCode']));
         }
       });
     }
  
positive.code: 
      try {
        final gist = await loader.loadGist(id);
        context.dartSource = gist.getFile('main.dart')?.content ?? '';
        context.htmlSource = gist.getFile('index.html')?.content ?? '';
        context.cssSource = gist.getFile('styles.css')?.content ?? '';
        context.testMethod = gist.getFile('test.dart')?.content ?? '';
        context.solution = gist.getFile('solution.dart')?.content ?? '';
        context.hint = gist.getFile('hint.txt')?.content ?? '';
        tabController.setTabVisibility(
            'test', context.testMethod.isNotEmpty && _showTestCode);
        showHintButton?.hidden = context.hint.isEmpty;
        solutionTab?.toggleAttr('hidden', context.solution.isEmpty);
        editorIsBusy = false;
  
        if (analyze) {
          _performAnalysis();
        }
      } on GistLoaderException catch (ex) {
        // No gist was loaded, so clear the editors.
        context.dartSource = '';
        context.htmlSource = '';
        context.cssSource = '';
        context.testMethod = '';
        context.solution = '';
        context.hint = '';
        tabController.setTabVisibility('test', false);
        showHintButton?.hidden = true;
        solutionTab?.toggleAttr('hidden', true);
        editorIsBusy = false;
  
        if (ex.failureType == GistLoaderFailureType.gistDoesNotExist) {
          await dialog.showOk('Error loading gist',
              'No gist was found matching the ID provided ($gistId).');
        } else if (ex.failureType == GistLoaderFailureType.rateLimitExceeded) {
          await dialog.showOk('Error loading gist', 'GitHub\'s rate limit for '
              'API requests has been exceeded. This is typically caused by '
              'repeatedly loading a single page that has many DartPad embeds or '
              'when many users are accessing DartPad (and therefore GitHub\'s '
              'API server) from a single, shared IP address. Quotas are '
              'typically renewed within an hour, so the best course of action is '
              'to try back later.');
        } else {
          await dialog.showOk('Error loading gist', 'An error occurred while '
              'loading Gist ID $gistId.');
        }
      }
    }
  
    void _handleExecute() {
  
negative.code:     }
  
      if (context.dartSource.isEmpty) {
        dialog.showOk(
            'No code to execute',
            'Try entering some Dart code into the "Dart" tab, then click this '
                'button again to run it.');
        return;
      }
  
  