raised-bed Weed barrier under or over dirt in raised beds?

Pretty much just the question in the title. I want to keep weeds under control, but I also don't want to mess up the potential for root development. The weed barrier I'm looking at is supposed it be good for drainage, so that's not a concern. The beds are 1 foot deep. Here's the link:
Should that go over or under the dirt? Or both, so that it warms the soil, too? Any help is much appreciated.
Over and I use landscape staples to hold it down - no weeding is such a joy!