- Changed DEPEND case separator from ':' to 'THEN'
- Added a new attribute type, set, declared using '{' and '}'
- Added a new interpretation of 'IN' which refers to sets
- Upgraded loop and aggregation filters to use 'IN' both for containers and sets
- Added messages for UNDO responses
- Added UNDO as a response to QUIT
- Empty player input is now interpreted as forfeiting that command turn