anchor.diff:      if (href != null && href != '') return;
   
       // TODO(sigmund): warn also if href can't be resolved.
  -    _logger.warning('link rel="$rel" missing href.', node.sourceSpan);
  +    _logger.warning('link rel="$rel" missing href.', span: node.sourceSpan);
     }
   
     /** Produce warnings if using `<element>` instead of `<polymer-element>`. */
     void _validateElementElement(Element node) {
       _logger.warning('<element> elements are not supported, use'
  -        ' <polymer-element> instead', node.sourceSpan);
  +        ' <polymer-element> instead', span: node.sourceSpan);
     }
   
     /**
  
positive.code:   void _validatePolymerElement(Element node) {
      if (_inPolymerElement) {
        _logger.error('Nested polymer element definitions are not allowed.',
            node.sourceSpan);
        return;
      }
  
  
negative.code:       var newName = toCamelCase(name);
        _logger.warning('PolymerElement no longer recognizes attribute names with '
            'dashes such as "$name". Use "$newName" or "${newName.toLowerCase()}" '
            'instead (both forms are equivalent in HTML).', span: span);
        return false;
      }
      return true;
  