Differences between VoiceXML and VoXML

Hi All!
I've just started looking at this area and would be grateful if someone would explain why Motorola seem to have their own version of VoiceXML which they call VoXML, and what the main differences, advantages, and disadvantages of using each would be?

I would be grateful for any information on comparisons!

Thanks!
Richard
richard.palfery@smarttrust.com
UK