I just pushed a big revamp of how we generate calendar ICS files, something I've been working on for the past week. ICS files are the attachments in #cal-invite and #cal-reminder messages and are also what's sent out when you subscribe to a Groups.io calendar (with your Outlook/Gmail/Yahoo/etc calendar). They describe calendar events and are what allow you to easily add events from your Groups.io calendar to your Gmail/Outlook/Yahoo/etc calendar.
<NerdTalk> The changes affect how we described repeating events in the ICS files. The way we did it before was to just describe the individual events that happen; now we describe the repeating event criteria instead (ie happens every Monday at 10am). </NerdTalk>
The end result is that, in your Google calendar for example, it will know a specific event is part of a repeating event, so that you can delete all of them at once. Also, importantly, cancel event notices should behave much better.
These changes should not affect how your calendar behaves on Groups.io. These are just changes to ICS files. Mostly, you should not notice any changes. If you do, please let me know off list. Calendar changes are notoriously difficult to test, because of all the different calendars out there and also, to me, the ICS spec is difficult to implement correctly.
(also I added a new #update hashtag for these kinds of announcements)