[[!Referer]]
if(isset($_SESSION['referId'])){
$referId = $_SESSION['referId'];
}else{
$referId = 0;
}
$thisId = $modx->resource->get('id');
$_SESSION['referId'] = $thisId;
if($referId){
$url = $modx->makeUrl($referId);
return '<a href="'.$url.'">Назад</a>';
}else{
return '';
}
или
<input type="button" onclick="history.back();" value="Назад"/>или
<a href="javascript:history.back();">Назад</a>