anchor.diff:      return (element.offsetWidth != 0 && element.offsetHeight != 0);
     }
   
  -  _focusDefault() {
  +  void _focusDefault() {
       if (_autoFocusDirective != null) {
         _autoFocusDirective.focus();
       } else if (_content != null) {
  
positive.code:     _disposer.dispose();
    }
  
    focusFirst() {
      _focusFirstInOrder(
          new DomTreeIterator(_content.element, scope: _content.element));
    }
  
    focusLast() {
      _focusFirstInOrder(new DomTreeIterator(_content.element,
          scope: _content.element, reverse: true, wraps: true));
    }
  
    _focusFirstInOrder(Iterator<Element> iterator) {
      while (iterator.moveNext()) {
        if (iterator.current.tabIndex == 0 && _visible(iterator.current)) {
          iterator.current.focus();
  
negative.code: 
  @Directive(
    selector: '[focusContentWrapper]',
  )
  class FocusContentWrapper extends FocusableDirective {
    Element _element;
  