Set cursor in text_field_tag?


Let’s say I’ve text_field_tag A and B.

I type something in A and hit the tabulator-key. An observe_field-
helper-method gets triggered, some fancy Ajax-JS-stuff happens, the
formerly disabled field B gets enabled and now I’m able to type into
textfield B.

No, how can I say with JS/Prototype/Railshelpers that I’d like the
cursor to jump right in textfield B after the Ajax-JS-stuff happend?
So the user can just write along after hitting the tab-key and
changing from A to B?