resizable <textarea> is generally quite a limited thing.

It would be significantly more useful if we would have universal <frameset>:

   <frameset cols="200px,*>
     <select type="list">...</select>
     <textarea>...</textarea>
   </frameset>

so to have split views.

Resizable textareas are quite trivial to implement with barebone JS but such split views require native support from browsers in order resizing to work effectively.