Page is a not externally linkable
g1smd - 8:01 pm on Aug 5, 2007 (gmt 0)
It is up to the user agent to resolve http://www.domain.com/folder/ and ../whatever/somepage.html to the correct fully qualified URL. I wouldn't chance a bot getting it wrong. I never use ../../somepage.html style URLs. I always begin with a trailing / and count from the root.
The base tag sets the base URL that relative links from that page will use.