How to do nothing ? :)

[eluser]jonez[/eluser]
Are you using AJAX? In your key binding make an AJAX call to see if you should change pages, in the callback if you receive true (yes) redirect the user using [removed]. If false (no) do nothing.

If you do it only using PHP you'll have to store the previous URL in a session/cookie (or use the agent referrer) and redirect back to the previous step when you hit your false condition.