Return reference filed under rtype/label

         The references are organized by field/label, e.g. category/cat1.
         This lets us use a shorthand notation to go the resource, e.g.
         ref:category:cat1 instead of folder1/folder2/cat1.

def get_reference(self, rtype: str, label: str):
        """ Return reference filed under rtype/label

         The references are organized by field/label, e.g. category/cat1.
         This lets us use a shorthand notation to go the resource, e.g.
         ref:category:cat1 instead of folder1/folder2/cat1.
         """

        # We are doing this instead of dictionary access in case we change
        # the storage later to a multidict thingy for optimization.

        reftype = self.data.get(rtype)
        if reftype:
            # The reftype might be "python" or "sphinx" or something else
            # from an Intersphinx registry, not something internal to
            # Kaybee.
            return reftype[label]