def peek(self, iroute: "InstanceRoute") -> Optional[Value]:
        """Return a value within the receiver's subtree.

        Args:
            iroute: Instance route (relative to the receiver).
        """
        val = self.value
        sn = self.schema_node
        for sel in iroute:
            val, sn = sel.peek_step(val, sn)
            if val is None:
                return None
        return val
Return a value within the receiver's subtree.

        Args:
            iroute: Instance route (relative to the receiver).