Ok everyone: it is a zope bug.
The following should be included in zope.app.schema.fields.zcml:
description="Date Field" />
<require like_class="zope.schema.Orderable" />
<require like_class="zope.schema.Field" />
PS -- Jim -- I sent in my contributor form almost two weeks ago? Have
you received it yet? I'd be happy to put this in myself, if I could.
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