TYPO3 Core

This is the signature of t3lib_div::devLog

    /**
     * Logs message to the development log.
     * This should be implemented around the source code, both frontend and backend, logging everything from the flow through an application, messages, results from comparisons to fatal errors.
     * The result is meant to make sense to developers during development or debugging of a site.
     * The idea is that this function is only a wrapper for external extensions which can set a hook which will be allowed to handle the logging of the information to any format they might wish and with any kind of filter they would like.
     * If you want to implement the devLog in your applications, simply add lines like:
     *         if (TYPO3_DLOG)    t3lib_div::devLog('[write message in english here]', 'extension key');
     *
     * @param    string        Message (in english).
     * @param    string        Extension key (from which extension you are calling the log)
     * @param    integer        Severity: 0 is info, 1 is notice, 2 is warning, 3 is fatal error, -1 is "OK" message
     * @param    array        Additional data you want to pass to the logger.
     * @return    void
     */
    public static function devLog($msg, $extKey, $severity = 0, $dataVar = FALSE) {
    }

Notice that the last Parameter is declared as array, but defaults to FALSE. This leads to warning notices in IDEs like PHPStorm when you use devLog.