docs: private LogNode addChild(final String sortKey, final String msg, final long elapsedTimeNanos,
              final Throwable exception) {
          final String newSortKey = sortKeyPrefix + "\t" + (sortKey == null ? "" : sortKey) + "\t"
                  + String.format("%09d", sortKeyUniqueSuffix.getAndIncrement());
          final LogNode newChild = new LogNode(newSortKey, msg, elapsedTimeNanos, exception);
          newChild.parent = this;
          // Make the sort key unique, so that log entries are not clobbered if keys are reused; increment unique
          // suffix with each new log entry, so that ties are broken in chronological order.
          children.put(newSortKey, newChild);
          return newChild;
      }