Hi Dan,
I tried this code and I have a little problem.
I add 'reservations' table one column: relatedKey int(10) unsigned	
The default value is 0 (zero) so that I can identify those reservations that do not belong to any group
I updated the value of three reservations to 1 (eg. Group 1)
But before any 'Highlighting Related Reservations', I get a Delete symbol and an Info bubble.
Delete event is handled by (Hover)
           dp.onBeforeEventRender = function(args) {
                // Event Delete handler to prevent build-in grey X for deletion
                args.e.areas =
                [{ bottom: 4, right: 4, width: 15, height: 15, v: "Hover",
                style: "background-image:url('icons/erase.png')",
                action: "JavaScript",
                js: function(e) {
                    var args = {};
                    args.e = e;
               // ...
Bubble is regular DayPilot
dp.bubble = new DayPilot.Bubble({});
Since I cannot post attachments through this, I will send them separately via email.
Best regards,
Jorma