Dynamic XMLList

if I have this…

var base:XML = XMLfile.someNode;

var foo:XMLList = base.service.testTest.sb.description;

…and everything works so far, but then I need to pass a variable to replace the “sb” node, how can I essentialydo this:

var foo:XMLList = base.service.testTest. + someVar + .description;

I know you can’t do it this way, but I’ve tried it too many different ways to post them all here and nothing works at all.