Thanks for that. I actually found that knowledgebase article about half an hour after I made that post and it was very helpful.
I've now got the Recurring appointment hidden or shown depending which Room (resource) the appointment is opened on.
I would like to change the visibility if the Room dropdown box is changed, otherwise I may get the situation where the user opens a new appointment for a room that can have recurring appointments, and then changes the dropdown to a room that cannot. A clientside event perhaps?