What data can FO output that is considered to be an extension to GEDCOM?
Any data beyond the ones defined in the 5.5 specification (plus their substructures) could be considered an extension. GEDCOM defines an extension as starting with an _ character to indicate that this is known not to be directly supported by GEDCOM. Examples in FO 6.0 include the email tag used in the submittor record and the address record and the _NAME tag used in the address record. I really like these extensions and GEDCOM will probably adopt EMAIL as a standard in the future. In 7.0 the TODO list is an extension as is the correspondence log.
