======Synopsis:======
[[on]] [<modes>]pong [<serial#>] [-|^]<match> { <action> }

======Description:======
This hook is triggered whenever the client receives a protocol PONG
message.  Under normal circumstances, the sender will be a server.
However, clients are also allowed to send PONG messages to each other.
Since there is never any reason for a client to send a PONG to another
client, this hook can be useful for blocking PONG floods.

======Parameters:======
|$0     |nickname sending the PONG                                          |
|$1-    |argument to PONG (usually the same as $0, but not necessarily)     |

======Examples:======
To filter PONG messages from other clients:
   on ^pong "*" {
      if ( rmatch($0 %.%) ) {
         xecho -b Received protocol PONG from $0: $1-
      }
   }