It resizes the textarea when moving the div.grippie. How?
They use TextAreaResizer.
You can find the Stack Exchange version on their Development CDN as part of
In that source from
jquery.textarearesizer.js onward you'll find:
jQuery TextAreaResizer plugin Created on 17th January 2008 by Ryan O'Dell Version 1.0.4
The current internal SE version is
1.0.5 Fixed a bug in dynamic html and IE7 - Geoff Dalgas