SimpleDALRegExt and product-type

[Markus Demleitner]

Dear Registry,

Just FYI, there's a new PR of SimpleDALRegExt out now that does what
I talked about the other day:

On Fri, Sep 24, 2021 at 09:07:56AM +0200, Markus Demleitner wrote:
> Hence, I believe we will not see a usable product-type vocabulary any
> time soon, and with that, we could either add productType with a
> custom (i.e., in-schema) constraint or just drop it.

See <https://ivoa.net/documents/SimpleDALRegExt/20211004/>.

In case anyone wants to add community review comments,
https://wiki.ivoa.net/twiki/bin/view/IVOA/SimpleDALRegExtV12RFC is
there for you.

        -- Markus