I have an application that connects to SQL Server clustered instance and
works based on the fact whether it is installed on active SQL node or passive
SQL node.

I have found fn_virtualservernodes() function that returns the list of
failover nodes. I have observed that the first node returned by this
function's resultset is active node. But this is not documented.
Is this assumption right?
Can you point me to any documentation that ascertains this beahvior?

Also is there any other method through which my application can ascertain if
it is running on active node.

TIA