code: function()
  		{
  			var isVisible = ( this.$.offsetHeight || this.$.offsetWidth ) && this.getComputedStyle( 'visibility' ) != 'hidden',
  				elementWindow,
  				elementWindowFrame;
  
  			// Webkit and Opera report non-zero offsetHeight despite that
  			// element is inside an invisible iframe. (#4542)
  			if ( isVisible && ( CKEDITOR.env.webkit || CKEDITOR.env.opera ) )
  			{
  				elementWindow = this.getWindow();
  
  				if ( !elementWindow.equals( CKEDITOR.document.getWindow() )
  						&& ( elementWindowFrame = elementWindow.$.frameElement ) )
  				{
  					isVisible = new CKEDITOR.dom.element( elementWindowFrame ).isVisible();
  				}
  			}
  
  			return !!isVisible;
  		}
docs: Checks if this element is visible. May not work if the element is
  child of an element with visibility set to "hidden", but works well
  on the great majority of cases.
  @return {Boolean} True if the element is visible.