php setcookie domain

Question

Some application, not written by me, and not in PHP, creates a cookie for the domain \"www.domain.com\".

I am trying to replace that cookie. So in php I did:

Answer 1

If you specify a domain, you should follow RFC 2109 and prefix the domain with a dot; otherwise the client will do that. But if you don’t specify a domain at all, the client will take the domain of the request.