docs: public synchronized void modified(Properties props) {
  
          for (Object key : props.keySet()) {
              String msgId = (String) key;
              String logHandlerIds = props.getProperty(msgId);
  
              Set<String> logHandlerIdSet = getOrCreateLogHandlerIdSet(msgId);
  
              // "logHandlerIds" is a comma-separated list of LogHandlers IDs. Each LogHandler ID
              // may contain a +/- char in front, to indicate that the LogHandler should be 
              // added/removed to/from the list for this msgId. If the +/- is not specified, 
              // assume +.
              for (String id : split(logHandlerIds, ",")) {
  
                  // Protect against bad input, such as empty IDs.
                  id = id.trim();
                  if (id.length() > 0) {
                      // Check for the +/- in first char.
                      char plusOrMinus = id.charAt(0);
                      if (plusOrMinus != '+' && plusOrMinus != '-') {
                          plusOrMinus = '+'; // + by default.
                      } else {
                          id = id.substring(1); // skip over the +/-.
                      }
  
                      // Make sure there's still something left after stripping off the +/-.
                      if (id.length() > 0) {
                          if (plusOrMinus == '+') {
                              logHandlerIdSet.add(id);
                          } else {
                              // '-' means remove.
                              logHandlerIdSet.remove(id);
                          }
                      }
                  }
              }
  
              if (logHandlerIdSet.size() == 1 && logHandlerIdSet.contains("DEFAULT")) {
                  // No entries (other than default) for this msgId.  Remove it from the map.
                  msgIdToLogHandlerIds.remove(msgId);
              }
          }
      }