Type: String
Identifies beginning of new message and protocol version. ALWAYS FIRST FIELD IN MESSAGE. (Always unencrypted)
Added in protocol FIX.2.7
See in: FIX.4.0, FIX.4.1, FIX.4.2, FIX.4.4, FIX.5.0, FIX.5.0SP1, FIX.5.0SP2, FIX.5.0SP2 EP240, FIXT.1.1.