[brute]

The best interface I have seen yet allows you to switch between source and rendered text on a paragraph-to-paragraph basis[1]. There is really no reason why the text you are currently NOT editing should not be rendered. Unfortunatly this approach is a little bit more challenging to implement, why so few editors use it.

That said, I fully agree with your stance on double-pane editors.

[1] http://www.inkcode.net/qute

[bjeanes]

I have long held the same opinion as the parent comment and even attempted to build it myself a few times, but I hadn't seen qute, and I think I like that approach even better. Well, a hybrid; the paragraph currently being edited could be highlighted as markdownify does.