public function setAddValidators($v)
    {
        $validKeys = array_keys(self::$validatorBitMap);

        // lowercase input
        $v = strtolower($v);

        $bits = self::VALIDATORS_NONE;

        $exprs = explode(',', $v);
        foreach ($exprs as $expr) {
            $expr = trim($expr);
            if (!empty($expr)) {
                if (!isset(self::$validatorBitMap[$expr])) {
                    throw new BuildException("Unable to interpret validator in expression ('$v'): " . $expr);
                }
                $bits |= self::$validatorBitMap[$expr];
            }
        }

        $this->validatorBits = $bits;
    }