It uses queryCommandState(), which is a deprecated browser feature [1]. It's quite common in many simpler WYSIWYG editors. Thing is, it might be so widespread that some people claim that it will never be truly deprecated.

OverType doesn't use this and the result is that you gotta build all the features in JS.

[1]: https://developer.mozilla.org/en-US/docs/Web/API/Document/qu...