A permissioned-data space type for calendar apps to share. A space holds events and the RSVPs to them. Each account keeps its own records, so a space may hold one event or many, from one author or several. The space authority can always add records; who else can is up to the space's policy. Key is any. Default collections are the existing calendar.event and calendar.rsvp, whose shape doesn't change.
Prior art: https://ngerakines.leaflet.pub/3mqxalpvn4k2e Discussion: https://discourse.atmosphere.community/t/should-calendar-apps-share-a-space-type/1445