Policy URL

[rmartini@iis.com.br]

I found  at the gpg an original flag "--set-policy-url". 
What's this? 
Well, I can understand this option literally... 
But, the RFC 2440 tell us about this:

"5.2.3.19. Policy URL
This subpacket contains a URL of a document that describes the policy
that the signature was issued under."

Someone wrote or knows a simple example of this document? The "Policy" above decribed means
the limitation or validity of the signature?

Thanks

Renato Martini ::: rmartini@cipsga.org.br
RIO DE JANEIRO ::: BRASIL