Sample code:
(If viewing the code below in Google Groups, ignore the leading and trailing backticks; those are just to keep the code “unprocessed” at Talk TW.)
<style>
.wide100 {width:100%}
.bspace {margin-bottom:-18px;}
</style>
<div style="border:4px double lightgray;">
<$edit-text class="wide100 bspace" tiddler="AppSettings" field="myconfig" tag="textarea">
<details><summary>Multi-line Edit Toolbar</summary>
This space does not have to be just for buttons. It can be for all sorts of things. Like helpful tips, reminders, whatever.
</details>
</$edit-text>
</div>