question on portupgrade and FreeBSD branches

[rain cip]

Hello,
 
I am new to the FreeBSD ports collection system and am having some difficulty understanding how the ports collection works with the FreeBSD branches.  After having perused the ports collection doc on the FreeBSD website, I got the impression that it is the FreeBSD branch tag that determines which versions of the packages or ports will be installed/upgraded.  But this is somehow confusing to me when I need to upgrade a port.  Here is an example.  I have FreeBSD 5.3 installed via CD so it appears to me that the "branch tag" used by my installation is 5.3-RELEASE.  I installed a bunch of packages from the CD, then updated the ports collection using the CVSup.  Now, if I use portupgrade to upgrade a package, on which branch will it look for the new ports?  
 
One example is KDE.  I had version 3.3.0 installed via the ports collection but now there is a new 3.3.1 version out there, which appears to be on the 5.3 STABLE branch.  But can I simply use the portupgrade on my 5.3-RELEASE to upgrade KDE to the 3.3.1 port? 
 
rain
 

		
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