private function getConfigKeys()
    {
        if (isset($this->configKeys)) {
            return $this->configKeys;
        }
        $this->configKeys = array(
            'debug' => array(
                // any key not found falls under 'debug'...
            ),
            'abstracter' => array(
                'cacheMethods',
                'collectConstants',
                'collectMethods',
                'objectsExclude',
                'objectSort',
                'useDebugInfo',
            ),
            'errorEmailer' => array(
                'emailBacktraceDumper',
                // 'emailFrom',
                // 'emailFunc',
                'emailMask',
                'emailMin',
                'emailThrottledSummary',
                'emailThrottleFile',
                'emailThrottleRead',
                'emailThrottleWrite',
                // 'emailTo',
                'emailTraceMask',
            ),
            'errorHandler' => \array_keys($this->debug->errorHandler->getCfg()),
            'output' => array(
                'addBR',
                'css',
                'displayListKeys',
                'filepathCss',
                'filepathScript',
                'onOutput',
                'outputAs',
                'outputAsDefaultNonHtml',
                'outputConstants',
                'outputCss',
                'outputHeaders',
                'outputMethodDescription',
                'outputMethods',
                'outputScript',
            ),
        );
        return $this->configKeys;
    }