“where did you find documentation on the sender and event args objects in the PageRequestManager events?”
To answer the question: I didn’t. However, I can show you something even better.
Exploring ASP.NET AJAX with Firebug
Let’s say I’m interested in learning more about the InitializeRequest event and how to find out the ID of the control that fired it. So, I’m going to set a breakpoint inside my InitializeRequest event handler, by clicking the left margin of the window beside a line in the handler:
Right away, I find what I was looking for: args._postBackElement.id contains a string with the name of the button that fired the event.
Don’t stop there!
You can’t see it in the screenshot, but there is a wealth of information in these objects. I would encourage anyone who is serious about ASP.NET AJAX framework development to take a few minutes and really dig through them this way. It’s hard to beat the power of learning by seeing and touching something, as opposed to just reading about it.
Don’t forget to also take a look at the PageRequestManager object itself. As the underpinning of the entire framework, it has some very useful methods and properties.