protected function enumValuesFromCheckClause($clause)
    {
        $segments = preg_split('/ +OR *\[/i', $clause);
        $constraints = array();
        foreach ($segments as $segment) {
            $bits = preg_split('/ *= */', $segment);
            for ($i = 1; $i < sizeof($bits); $i += 2) {
                array_unshift($constraints, substr(rtrim($bits[$i], ')'), 1, -1));
            }
        }
        return $constraints;
    }