(author-date) local styles

So on the zotero forums someone asked for a feature I myself have been
waiting for: the ability to speecify local styles such that I can get
"Doe (1999)."

This remind me of one of the reasons for my original design and one of
the potential downsides to the new design. If the styles no longer have
a concept of author-date styles, and validation is no longer
conditioned on that class, how is an implementation to know what to do
if the local style is set to “year-only” (or some such)?

In the earlier schema, and author and date element were required in the
citation definition.