Why HTML in the edit area?

In the edit area where one writes messages, there is some HTML, namely this:

<div data-slate-object="block" data-key="31" style="position: relative;"><span data-slate-object="text" data-key="32"><span data-slate-leaf="true" data-offset-key="32:0"><span data-slate-zero-width="z" data-slate-length="0"><br></span></span></span></div>

This makes it inconvenient to use plugins such as "Edit with Emacs", because if you replace that HTML with just text, the text area breaks. Can't you keep the edit area free of inner HTML?