explain the usage of versions with regards to payment code behavior

Author: justusranvier

bip-0047.mediawiki

@@ -84,7 +84,19 @@ Hardened derivation is used at this level.
 
 Except where noted, all keys derived from a payment code use the public derivation method.
 
-==Standard Payment Codes (v1)==
+==Versions==
+
+Payment codes contain a version byte which identifies a specific set of behavior.
+
+Unless otherwise specified, payment codes of different versions are interoperable. If Alice uses a version x payment code, and Bob uses a version y payment code, they can still send and receive transactions between each other.
+
+Currently specified versions:
+
+* Version 1
+** Address type: P2PKH
+** Notification type: address
+
+==Version 1==
 
 ===Representation===
 
@@ -127,6 +139,8 @@ It is assumed that Alice can easily obtain Bob's payment code via a suitable met
 
 Prior to the first time Alice initiates a transaction to Bob, Alice MUST inform Bob of her payment code via the following procedure:
 
+Note: this procedure is used if Bob uses a version 1 payment code (regardless of the the version of Alice's payment code). If Bob's payment code is not version 1, see the appropriate section in this specification.
+
 # Alice constructs a transaction which sends a small quantity of bitcoins to Bob's notification address (notification transaction)
 ## The inputs selected for this transaction MUST NOT be easily associated with Alice's notification address
 # Alice derives a unique shared secret using ECDH: