vote on issue #152 Add schematron rules for productionset reference constraints

[Bob Stayton <bobs@sagehill.net>]

Issue 152, Add schematron rules for productionset reference constraints. Norm says "In a productionset there are a couple of referential integrity constraints that should be checked with Schematron, <productionrecap> and <constraint>." https://github.com/docbook/docbook/issues/152

I think this is a useful addition, and I don't see any negative consequences. If there are no objections, I move to accept this change. Scott can second it and vote, and other voting TC members can vote. I vote yes.

-- 
Bob Stayton
bobs@sagehill.net