Of course, we don't really want every event; for any but the smallest sites, this would quickly crowd the calendar to uselessness. We would like to limit the site-wide calendar to the most noteworthy events, omitting specialty items like assignments that apply to only one in a hundred people. (For that matter, typical visitors won't think of assignments as "events" at all and would be surprised to see them on the calendar.) There are several ways to indicate an event's noteworthiness without resorting to much coding:
Copy the Event type to make a new but identical type called something like "Site-Wide Event", either by writing a product or by simply copying and pasting within the
portal_typestool, accessed through Site Setup → Zope Management Interface. Have the Events collection find only instances of the new type. When considering this approach, note that an Events portlet will show only events of the original type. A partial workaround is to...