Syntax rules for my own EDI schema?

How do I create the EDI syntax rules using the method described by microsoft for creating an EDI schema not supplied with BizTalk?

For example, take a PO1 segment. X12 states that if either PO1_06 or PO1_07 is used, the other must be present. I don’t see any mention of how to implement this in the Microsoft KB article.

I don’t want to go to production with an EDI translator that is not fully featured, otherwise I’ll just be pushing my EDI problems off on my partners. So can someone explain how to implement these rules?