anchor.diff:    }
   }
   
  -CompareLevel _compareResult(
  -    CommonMarkTestCase expected, bool verboseFail, bool verboseLooseMatch,
  +CompareLevel _compareResult(String baseUrl, CommonMarkTestCase expected,
  +    bool verboseFail, bool verboseLooseMatch,
       {ExtensionSet extensionSet}) {
     String output;
     try {
       output = markdownToHtml(expected.markdown, extensionSet: extensionSet);
     } catch (err, stackTrace) {
       if (verboseFail) {
  -      printVerboseFailure(
  -          'ERROR', expected, expected.html, 'Thrown: $err\n$stackTrace');
  +      printVerboseFailure(baseUrl, 'ERROR', expected, expected.html,
  +          'Thrown: $err\n$stackTrace');
       }
   
       return CompareLevel.error;
  
positive.code: 
  String indent(String s) => s.splitMapJoin('\n', onNonMatch: (n) => '    $n');
  
  void printVerboseFailure(
      String message, CommonMarkTestCase test, String expected, String actual) {
    print('$message: http://spec.commonmark.org/0.28/#example-${test.example} '
        '@ ${test.section}');
    print('input:');
    print(indent(test.markdown));
  
negative.code: 
    final testPrefix = options['flavor'];
  
    var baseUrl = 'http://spec.commonmark.org/0.28/';
    ExtensionSet extensionSet;
    if (testPrefix == 'gfm') {
      extensionSet = ExtensionSet.gitHub;
      baseUrl = 'https://github.github.com/gfm/';
    }
  
    var sections = _loadCommonMarkSections(testPrefix);
  