The earliest ReactDOM version here, v14, was using extra span elements to wrap portions of the textual content. v15 had an update and replaced extra spans with comment nodes, like <!-- react-text: 9 -->. The latest version, v16, is now using nothing but the plain-old text nodes to keep-up-with updates.
Note: v17 haven’t updated demarcation method. It is same with previous version. It seems it is mature enough for now.