Your comments

Yes. We described the Vertabelo XML format in one of our blog article - Vertabelo XML version 2.1

At the begging of this article you also find link to the Vertabelo XSD.
We don't hear any feedback so I close the issue.
We have just enhanced our knownledge base section.
You are right. Both parameters have to be set or neither. We will add validation check. Thanks for pointing this.