anchor.diff:            }
           }
           return true;
  -      },
  -          failedAt(currentElement,
  -              "Invalid current element: $element [$begin,$end]."));
  +      }, failedAt(currentElement, message));
       }
       return new SourceSpan.fromTokens(uri, begin, end);
     }
  
positive.code:             }
              token = token.next;
            }
            return sb.toString();
          }
  
          if (element.enclosingClass != null &&
  
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 == '>' &&
  