mention reading RPL_WELCOME to get the assigned nick

index.md

@@ -448,6 +448,7 @@ Additionally, some servers also send a {% message PING %} and require a matching
 
 Upon successful completion of the registration process, the server MUST send, in this order, the {% numeric RPL_WELCOME %}, {% numeric RPL_YOURHOST %}, {% numeric RPL_CREATED %}, {% numeric RPL_MYINFO %}, and at least one {% numeric RPL_ISUPPORT %} numeric to the client. The server SHOULD then respond as though the client sent the {% command LUSERS %} command and return the appropriate numerics. If the user has client modes set on them automatically upon joining the network, the server SHOULD send the client the {% numeric RPL_UMODEIS %} reply. The server MAY send other numerics and messages. The server MUST then respond as though the client sent it the {% message MOTD %} command, i.e. it must send either the successful [Message of the Day](#motd-message) numerics or the {% numeric ERR_NOMOTD %} numeric.
 
+The first parameter of the {% numeric RPL_WELCOME %} message is the nickname assigned by the network to the client. Since it may differ from the nickname the client requested with the `NICK` command (due to, e.g. length limits or policy restrictions on nicknames), the client SHOULD use this parameter to determine its actual nickname at the time of connection. Subsequent nickname changes, client-initiated or not, will be communicated by the server sending a {% message NICK %} message.
 
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