See: http://requesttracker.wikia.com/wiki/ToggleCFs
"We had a need to show/hide custom fields depending on the value chosen for a certain "control" field. That is, if the control field had a certain value, we wanted to show a certain set of custom fields for editing and display. If the control field did not have that value, we wanted to hide those custom fields entirely. This could probably have been done easier in Javascript, but nobody on our team knows Javascript." -- RT Training - Dallas May 20-21 http://bestpractical.com/training
