From FF[3] to FF[4]

General

• Specification is more complete now
• Property identifiers consist only of uppercase (no lowercase in between allowed)
• Go-move/position defined for board sizes upto 52x52
• Rectangular boards possible.
• Compressed point lists for "list of point" PropValues
• Pass move may be specified as '[]'
• Text has been divided into two types: simpletext (basically a string) and text, which can be formatted (hard & soft linebreaks).
• Types for properties defined (move, setup, root, gameinfo, none). Therefore nodes can be divided into two types too: move / setup.
• Defined used charset (us-ascii) for property-identifiers and values. For SimpleText and Text charset is specified using CA property (default: ISO-latin-1)
• Property attribute 'inherit' defined.
• Time values are given in seconds
• Handling of unknown and illegal properties defined.

Properties no longer part of FF[4]

• CH (checkmark), SI (sigma), SE (moves in selftest), LT (lose on time), BS, WS, TC: are considered private to SGB
• ID (game-id) : serves no purpose (see specification of EV, RO instead)
• OM (#moves per overtime), OP (length of overtime)
• CI (chinese handicap) : not needed (HA doesn't imply fixed placement of handicap stones)
• OV (computer type property)
• RG, SC (obsolete markup)

New properties

• AP (application) : defines writer application
• ST (style) : for handling of comments and variations
• AR (arrow), LN (line), SQ (square) : new board markup
• OT (overtime) : gameinfo to describe byo-yomi rules
• CA (charset) : defines used charset for Text & SimpleText types
• DD (dimmed positons) : grey out the listed positions
• VW (view) : restrict view
• PM (print move) : defines how move numbers should be printed

Changed properties

• LB (label) may have more than 4 chars now (actually unlimited length)
• SZ (size) changed (rectangular boards possible now)
• Format of DT and RE is mandatory now (no longer just recommended)
• Some rule names are mandatory now.
• FG may contain some flags and a diagram name