Pocket Wizard Plus X compatibility

I have a set of PW Plus X's and need a few more, are they backwards compatible with the PW Plus?

Yes

"The PlusX is compatible with all Standard Channel-capable PocketWizard transmitters and receivers, so it's the perfect companion for your existing radios and new flashes."
http://www.pocketwizard.com/products/transmitter_receiver/plusx/