anchor.diff:        _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]);
  +          span: 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]);
  +          span: node.attributeSpans[name]);
       }
     }
   }
  
positive.code:       _logger.warning(
            'custom element "$customTagName" extends from "$baseTag". '
            'Did you mean to write <$baseTag is="$customTagName">?',
            node.sourceSpan);
      }
    }
  
  
negative.code:         // that the code is indeed using Dart.
          _logger.warning('script tag in polymer element with no type will '
              'be treated as JavaScript. Did you forget type="application/dart"?',
              span: node.sourceSpan);
        }
        if (src != null && src.endsWith('.dart')) {
          _logger.warning('script tag with .dart source file but no type will '
              'be treated as JavaScript. Did you forget type="application/dart"?',
              span: node.sourceSpan);
        }
        return;
      }
  