Question about (in progress) UBL 2.1

[Stephen Green <stephengreenubl@gmail.com>]

Nice to see that UBL 2.1 is coming along well.

Just a question regarding how it has been kept compatible with UBL 2.0:

Presumably the compatibility has been maintained at model level via
some rules of some sort but are these rules the fully published in the
latest customisation guide and if so, is that the one on the UBL TC home
page,
i.e. http://docs.oasis-open.org/ubl/guidelines/UBL2-Customization1.0cs01.pdf ?
If not, are rules for progressing from a UBL version 2.x to a version 2.x+1
going to be published?

Best regards

Steve
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Stephen D Green