attributeDomain should be required
The RC2 release shows attribute/attributeDomain as an oprional element. This
used to be required, and as far as I knew we agreed that it should be required.
It is a problem if it is optional, as people can leave out this truly
fundamental part of an attribute definition. Does anybody remember consciously
changing this? Can I change it back?
I'm reviewing an EML submission from an LTER site and they have omitted it for
all of their numeric attributes, which is clearly a problem! They also
consistently omit precision, which is also a problem, but I don't think it can
be required because it doesn't apply to nominal data.