XML is a modern file format and not yet much used in the Go world.
Jago is able to load and save Go games in XML format. Unlike SGF, which is a standardized format, such a standard does not exist for XML yet. The author of Jago created an own XML specification.
qGo is using Jagos XML definitions and currently able to load XML games saved with Jago. qGo is not yet able to save games in XML format, this but this feature will be implemented somewhen in the future.