This will be an enumerator just like the Behaviors property. It should, however, list the behaviors that are not allowed for the control. The common use case is that the developer does not want his popup to be resizable, so he/she needs only DisabledBehaviors="Resize" instead of listing all others that should be allowed in the Behaviors property.
On the server side the situation is pretty much similar. You could just subtract the extra behavior: radWindow.Behaviors -= Telerik.Web.UI.WindowBehaviors.Close; For the client-side you could use a bit of an improved approach: win.set_behaviors(win.get_behaviors() - Telerik.Web.UI.WindowBehaviors.Close) Hope this helps.
Nice workaround for the client side, Amandeep. I didn't realize you could do that one. I still like this idea for the server-side though.
why not try: var win=openradwindow(....); win.set_behaviors(-Telerik.Web.UI.WindowAutoSizeBehaviors.Close); note "-" before behaviour