I'm new to icalendar, but I couldn't find an answer to this specific situation.

My web site has a shared calendar where users can add and update events. They can also indicate on the web site if they will be attending an event. I want to add a button to let them download the calendar as published icalendar events.

When they indicated they will be attending an event, I want the event in the icalendar file to be set as "busy", otherwise as "not busy". So I can easily increment the sequence number on the event if the event is changed, but must I increment the sequence number if the user changed whether or not they will attend the event? I don't think that is a "mandatory" reason to increment the sequence, but I'm not sure. What will happen if the user changes their busy status for an event and re-downloads without the sequence number changing?

I suppose I can keep a separate sequence number for each time the user changes their attendance status, then add the event sequence number and attendance sequence number together for the "final" event sequence number that's downloaded, but do I have to do it that way?