private static function invokeErrorLogHandler($loggable, $level, array &$context) {
        if (!key_exists('cliMessage', $context))
            self::composeCliMessage($loggable, $level, $context);

        $msg = 'PHP '.$context['cliMessage'];
        if (key_exists('cliExtra', $context))
            $msg .= $context['cliExtra'];
        $msg = str_replace(chr(0), '?', $msg);                   // replace NUL bytes which mess up the logfile

        if (CLI && empty(ini_get('error_log'))) {
            // Suppress duplicated output to STDERR, the PrintHandler already wrote to STDOUT.

            // TODO: Instead of messing around here the PrintHandler must not print to STDOUT if the ErrorLogHandler
            //       is active and prints to STDERR.
            // TODO: Suppress output to STDERR in interactive terminals only (i.e. not in CRON).
        }
        else {
            error_log(trim($msg), ERROR_LOG_DEFAULT);
        }
    }