private $dati = array();
 
private function set($field, $offset, $value = array()) {
   if(!isset($this->dati[$field])) return false;
      if(!$this->isEmpty($value) AND $offset == 0) {
         array_unshift($this->dati[$field], trim($value));
         return true;
      } else if(is_numeric($offset)) {
         array_unshift($this->dati[$field], $this->dati[$field][$offset]);
         return true;
      } else {
         return false;
   }
}