You just have to have a globally unique id, so that if and when it's imported into another calendar application the entry can't be confused with another event. If you're not planning to use .ics email notifications or export bookings in .ics format then it doesn't matter what you use.
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You just have to have a globally unique id, so that if and when it's imported into another calendar application the entry can't be confused with another event. If you're not planning to use .ics email notifications or export bookings in .ics format then it doesn't matter what you use.