private function strAdd(string $str, string $insertstr, int $pos):string
    {
        $str = substr($str, 0, $pos) . $insertstr . substr($str, $pos);
        return $str;
    }
private function strAdd(string $str, string $insertstr, int $pos):string
    {
        $str = substr($str, 0, $pos) . $insertstr . substr($str, $pos);
        return $str;
    }
private function strAdd ( string $ str , string $ insertstr , int $ pos ) : string { $ str = substr ( $ str , 0 , $ pos ) . $ insertstr . substr ( $ str , $ pos ) ; return $ str ; }
Add string at specific postion
@param string $str String
@param string $insertstr string to add
@param int $pos Position
@return string The new string
Add string at specific postion