anchor.diff:            'this tag will not include the default properties of "$baseTag". '
             'To fix this, either write this tag as <$baseTag '
             'is="$customTagName"> or remove the "extends" attribute from '
  -          'the custom element declaration.', node.sourceSpan);
  +          'the custom element declaration.', span: node.sourceSpan);
         return;
       }
   
  
positive.code:       _logger.warning('Invalid event name "$name". After the "on-" the event '
            'name should not use dashes. For example use "on-$newEvent" or '
            '"on-${newEvent.toLowerCase()}" (both forms are equivalent in HTML).',
            node.attributeSpans[name]);
      }
  
      if (value.contains('.') || value.contains('(')) {
        _logger.warning('Invalid event handler body "$value". Declare a method '
            'in your custom element "void handlerName(event, detail, target)" '
            'and use the form $name="handlerName".',
            node.attributeSpans[name]);
      }
    }
  }
  
negative.code:           ' JavaScript event handler. Use the form '
            'on-event-name="handlerName" if you want a Dart handler '
            'that will automatically update the UI based on model changes.',
            span: node.attributeSpans[name]);
        return;
      }
  
      if (!_inPolymerElement) {
        _logger.warning('Inline event handlers are only supported inside '
            'declarations of <polymer-element>.',
            span: node.attributeSpans[name]);
      }
  
      var eventName = name.substring('on-'.length);
  