def find(self, node=None, category=None):
        """Returns a map of all entries with matching node and/or category. If both are None, returns all entries."""
        return altsortdict(
            (
                ((node_, category_), data)
                for ((node_, category_), data) in self.contents.items()
                if node is None or node == node_
                if category is None or category == category_
            )
        )