关于MS ajax客户端javascript API

i am not very much familiar of MS ajax client side javascript API so i search google but did not get any url from where i can have tutorial like sort of for MS ajax client side javascript API. as example Sys.WebForms.PageRequestManager.getInstance(). this piece of code is related with MS-Ajax client side API. if anyone knows then please refer me.i am not very much familiar of MS ajax client s