static private PrintStream getTarget() {
        switch(TARGET_CHOICE) {
            case Stdout:
                return System.out;
            case Stderr:
            default:
                return System.err;
        }
    }
This system property controls the internal level of chattiness
of SLF4J. Recognized settings are "INFO", "WARN" and "ERROR". The default value is "INFO".
slf4j-api/src/main/java/org/slf4j/helpers/Reporter.java