I have a short function ... and it tags "$error" as unused, whilst it is used within the string ${error['index']} construct

function getErrorString($errorList) {
    $str = "";
    foreach ($errorList as $error) {
        $str .= "[errno ${error['errno']}]\n";
    }
    return $str;
}

It appears to be that indexed variables in conjunction wiht the ${...} construct provokes the problem.

Just using $error works as expected (no hint), as does ${error} and $error[1].  But ${error[1]} provokes it to be shown.