Many weird behaviours with text selection

The Rich Text demo have many weird behaviours with text selection when:

1. Triple-clicking
2. Dragging the mouse vertically
3. Shift+Up/Down
4. Resizing the viewport
5. Zooming the viewport

You can try all these 5 actions with the non-pretext paragraph at the top, then with the pretext-enabled paragraph below, and notice the inconsistencies. Also, compare all that to the pdf.js demo.

Links:

• https://chenglou.me/pretext/rich-note/
• https://mozilla.github.io/pdf.js/web/viewer.html