This is one of the smallest possible uses of the Lurch Web Platform.
Visit the live app here. It has almost no features beyond ordinary word processing. Try this:
- Highlight a section of text and click the
[ ]button on the toolbar. - You should see a group form, and report the number of characters inside the group.
- Groups are visible only when your cursor is inside them.
Read the (heavily commented) code here:
There is also a very simple build process.