Observe_field and onkeypress


For the :frequency param in the docs, it says:

The frequency (in seconds) at which changes to this field will be
detected. Not setting this option at all or to a value equal to or less
than zero will use event based observation instead of time based

I’d like my field to make an ajax call for the onkeypress event, rather
than every 1 second or so. I thought it might do this if I omited
:frequency, but it doesn’t seem to do anything. Is there a way to set