code: function createIframeShim( element )
  	{
  		if ( !CKEDITOR.env.ie || CKEDITOR.env.version > 6 )
  			return null;
  
  		var shim = CKEDITOR.dom.element.createFromHtml( '<iframe frameborder="0" tabindex="-1"' +
  					' src="javascript:' +
  					   'void((function(){' +
  						   'document.open();' +
  						   ( CKEDITOR.env.isCustomDomain() ? 'document.domain=\'' + this.getDocument().$.domain + '\';' : '' ) +
  						   'document.close();' +
  					   '})())"' +
  					' style="display:block;position:absolute;z-index:-1;' +
  					'progid:DXImageTransform.Microsoft.Alpha(opacity=0);' +
  					'"></iframe>' );
  		return element.append( shim, true );
  	}
docs: Adding an iframe shim to this element, OR removing the existing one if already applied.
  Note: This will only affect IE version below 7.