I would like to do in a multiline textarea, what the http:/www.facebook.com
multiline textarea does when you compose a new message (or reply to a message
in your inbox).

When you reach the end of the textarea, it automatically expands it downwards
(as opposed to the standard HTML behavior, which is to keep the size but to
activate the scrollbar inside the textarea. Works in IE and FF (at least).

I have tried to look at the facebook code, but its very hard to "penetrate".

Does anyone have an idea, how this is done and how I can do it?

Sorry I cant post pictures, but go to facebook and write a message to a
friend. And make sure you keep typing :-)

Thanks for any ...

I don't have any code to provide for you, but it is done with javascript. You
need to use javascript to detect the amount of characters typed in then use
javascript to dynamically set the size of the text area when the max amount of
characters is reached.

Jeff