how can postback use ajax.net beta2

in atlas

var postBack =new Sys.WebForms.PostBackAction();

postBack.set_target("ctl00_MainContentHolder_btnAccAdd");

postBack.set_eventArgument('');

postBack.performAction();

but beta2

Sys.WebForms.PostBackAction object not exist

how can i do it?

hello.

xml-script and actions are defined in the value-added bits. download the november ctp and install it. thena dd the previewscript.js file to your page and everything should work ok.
o~ thank you very much~~