List of event fields to include. If this list is absent then all fields are included. The entries may include '.' characters to indicate sub-fields. So 'content.body' will include the 'body' field of the 'content' object. A literal '.' character in a field name may be escaped using a '\'. A server may include more fields than were requested.
The format to use for events. 'client' will return the events in a format suitable for clients. 'federation' will return the raw event as received over federation. The default is 'client'.