value of author is determined by the type (MIME type) and should be either free text (text/plain) or VCard (text/directory) some time terms are start, end, updated, created, deleted (time value can be a dateTime or iCalendar) free text or VCard depending on the MIME type relationship terms can be within, contains, equals, disjoint, intersects, touches, crosses, overlaps some point terms are center, navigation point, entrance posList can have 2 or 3 coordinate sets. If 3, then the 3rd is altitude in meters, and srsName must be http://www.opengis.net/def/crs/EPSG/0/4979