[Zope] base tag

Hello, I've been asked to administer a Zope site, and I have a problem. On each page, a statement like <base href="http://mysite.dk/dir/" /> shows up. dir/ changes if I move to another directory. Yet nowhere in the code can I find such a statement. Is this a common thing for Zope to add or is there a function or property that usually sets this? Cheers Nik