Extending Server Controls?

I see this blurb on the tutorials section:

"Extend server controls or control extenders: You might create new behaviors for given server controls by implementing a server control that also implements the IScriptControl to render the ASP.NET "Atlas" client script and register with the ScriptManager in the Web page. Page developers will gain from specific new server-side controls without needing to write ASP.NET "Atlas" script or JavaScript."

This is great to hear, anyone know how this works? ie. I see it says I don't need to write script at all?

Let's say I wanted a input mask textbox - how would I 'extend' the TextBox using IScriptControl and do this code without writing script?

Hi,

check alsothis article from my blog for an introduction to extenders.