The iButtonControl interface enables the button to be used as the default button on the page. You can set the validation group for it, and even the PostBackUrl property.
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iButtonControl  
The iButtonControl interface allows the button to be used as the default button on the page. 

Allows text, image or both for designing of the button UI.
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Built-in presets make the button look like different office styles, toolbox, popup menu and other well known button types.
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Use built-in presets to mimic familiar button styles. 
Customize the button appearance. 

Customize the button by setting rounded corners, focus, hover, pressed, and default appearance settings.
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