> Every time someone releases a new rich text editor ... uses contentEdtiable
Sciter is using its own implementation (obviously).
contentEdtiable thing is indeed quite limited for general purpose WYSIWYG editor.
For example Web platform is missing transactional update [1] mechanism that allows to put custom DOM mutation groups into unified undo/redo stack.
Sciter's <htmlarea> element ( implement behavior:richtext - WYSIWYG ) allows to build specialized editors. For example it is used in Sciter.Notes [2].
[1] https://docs.sciter.com/docs/behaviors/behavior-richtext#ric...
[2] https://notes.sciter.com/