TextChange Handler not detecting lost Focus if no change to conten

[Guest]

I know that if I change the text on a textBox it would trigger the
textBoxChange event hadler. But how about if you don't want to change
anything on the textbox and just want to focus on it and then press return or
Tab to cause an event.
When I press return (without changing content) in a TextBox, a PostBack is
generated but I don't know how to handle the event. I don't know what the
event is.

Q2. Is there a way (upon postback) to figure out what event triggered the
postback?(i.e. which control on your form caused it?)

Thanks