[Zope] Using ".." and "."

[smileych@paradise.net.nz]

Everywhere I look on the tutorials, I see the use of URL0 (or 1 or 2 or 
whatever).
Is there any disadvantages of just using "." when referencing?
eg:
<dtml-call "RESPONSE.redirect('..')">
to go from "users\update\update_user" document to the "users\" folder

An interesting point is that if the document is the index_html, you would 
only use "." rather than ".."   eg:
<dtml-call "RESPONSE.redirect('.')">
to go from "users\update\" (the index_html of the update folder) to 
the "users\" folder

So, is this a bad way to reference? Is there any advantage in the URLx 
referencing?

Thanks :)
SmileyChris