Take a look at the help file (the help file has a fairly decent explanation of almost everything, you can view help on a specific topic by typing /help <topic> (in this case /help $v2))

Quote:
$v1 & $v2

Returns the first and second parameters of an if-then-else comparison. So, in the case of this comparison:

if (text isin sometext) { ... }

$v1 will return "text" and $v2 will return "sometext".