textarea
is specifically difficult to use in this manner, because you cannot observe it's content changing with MutationObservers, only with events.
Worse still, there is no signal at all for setting textarea.value
(which is what your binding will do).
If you want to use textarea
like this, suggest you expose a property on the mark-down
element for binding a value, and listen to events from the textarea
to monitor user edits.
<mark-down value="{{post}}">
<textarea></textarea>
</mark-down>