Set selected from list or instance of object or name.

        Over-writes existing selection

def selected(self, new):
        """Set selected from list or instance of object or name.

        Over-writes existing selection
        """
        def preprocess(item):
            if isinstance(item, str):
                return self.options[item]
            return item
        items = coerce_to_list(new, preprocess)
        self.widget.value = items