anchor.diff:              }
               token = token.next;
             }
  -          return sb.toString();
  +          message = sb.toString();
  +          return false;
           }
   
           if (element.enclosingClass != null &&
  
positive.code:           }
          }
          return true;
        },
            failedAt(currentElement,
                "Invalid current element: $element [$begin,$end]."));
      }
      return new SourceSpan.fromTokens(uri, begin, end);
    }
  
negative.code:       }
        Element element = currentElement;
        uri = element.compilationUnit.script.resourceUri;
        String message;
        assert(() {
          bool sameToken(Token token, Token sought) {
            if (token == sought) return true;
            if (token.stringValue == '[') {
              // `[` is converted to `[]` in the parser when needed.
              return sought.stringValue == '[]' &&
                  token.charOffset <= sought.charOffset &&
                  sought.charOffset < token.charEnd;
            }
            if (token.stringValue == '>>') {
              // `>>` is converted to `>` in the parser when needed.
              return sought.stringValue == '>' &&
  