RFC4791 section 7 specifies a query language for search queries, allowing caldav clients to fetch events for some date range, categories, etc.

SOGo seems to support this partially - simple date queries work, same with queries for all events or all tasks on a calendar, but most other queries fails or delivers the wrong result.

This is the simplest query, "give me everything on the calendar", and it returns nothing:

REPORT https://sogo.bekkenstenveien53c.oslo.no/SOGo/dav/test/Calendar/pythoncaldav-test/
Depth: 1
Content-Type: application/xml; charset="utf-8"

<?xml version='1.0' encoding='utf-8'?>
<C:calendar-query xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
  <D:prop>
    <C:calendar-data/>
  </D:prop>
  <C:filter>
    <C:comp-filter name="VCALENDAR"/>
  </C:filter>
</C:calendar-query>

This query should give me all events with CLASS set to CONFIDENTIAL, but it returns all events from the calendar:

REPORT https://sogo.bekkenstenveien53c.oslo.no:443/SOGo/dav/test/Calendar/pythoncaldav-test/
Depth: 1
Content-Type: application/xml; charset="utf-8"

<?xml version='1.0' encoding='utf-8'?>
<C:calendar-query xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
  <D:prop>
    <C:calendar-data/>
  </D:prop>
  <C:filter>
    <C:comp-filter name="VCALENDAR">
      <C:comp-filter name="VEVENT">
        <C:prop-filter name="CLASS">
          <C:text-match collation="i;octet">CONFIDENTIAL</C:text-match>
        </C:prop-filter>
      </C:comp-filter>
    </C:comp-filter>
  </C:filter>
</C:calendar-query>