Hi there,
You can't make direct enhancement to controls. However, you can develop your own server controls that inherit from an existing control. This way, you can enhance existing controls by adding properties and behaviors to them.
The MSDN has a great section about creating server controls. You can find the index of it
here, but there is quite a lot below this starting page that is worth studying.
Cheers,
Imar
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Imar Spaanjaars
Everyone is unique, except for me.