private void writeObject(final ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        s.writeInt(level);
        s.writeInt(syslogEquivalent);
        s.writeUTF(levelStr);
    }
Serialize level.

@param s serialization stream.
@throws IOException if exception during serialization.
log4j-over-slf4j/src/main/java/org/apache/log4j/Level.java