Limiting a TextArea
 

I'm working on a custom module that I really need to have a text area with set columns and rows.
Not just what is visible but actually limit the the input to 12 columns and 4 rows (for a digital sign).
I know that setting the visible limits is easy: Code:
$form->addTextarea('signmsg');
$form->setRows('signmsg', 4);
$form->setCols('signmsg', 12);
When I try to use the setsize for a text area: Code:
$form->setSize('signmsg', 12);
It doesn't work you can still type past the set columns and rows, you just get scroll bars.

So is there any way to limit input for a text area?