Re: WIP - xmlvalidate implementation from TODO list

Hey Jim and Pavel, thanks for demonstrating interest.

> XML is a little bit outdated - but the proposed infrastructure can be
used for any documents, so it can theoretically supports json, jsonb too
[...]. I expect something like XMLVALIDATE will be JSON standard in a few
years.

That doesn't sound like a bad idea to me. But I suspect I would need to
almost completely revamp the implementation in the patch so far, so I would
like to confirm a few things before committing to anything on that front.

I am still unsure how the permissions would be managed properly with the
API approach. It seems to me we could rely on the ACL like before, but I
sense there's something more arcane around it when it comes to the
extension.

I didn't realize, but DB2 actually gives you decomposition over an xml
hierarchy into tables, which is an insanely valuable feature. I wonder how
we could go with that here using the current catalog approach.

Is there anything else that might be troublesome with changing approaches?

Regards, Marcos.