There are two forms of the card command. The first form adds
a card to the list of available cards, and the second selects one of the
available cards as the one to be used.
The command to add a card is card +$CARDSPEC where the
$CARDSPEC is one of the following:
s:" followed the port number of
a Prosody S server.
x:" followed the IP address of a
Prosody X card.
When the command "card $N", where $N is a
number, selects the Nth card.
Currently, only the mod command uses the selected card.
This is a command understood by the pathtest test program.