Way to combine XML files in same namespace?

In mujoco XML we can compose files multiple ways: we can use `include` to bring in assets and `attach` to build hierarchies. I'm wondering if there's any equivalent to `include` in `dm_control.mjcf`.

My use case is I have both cartesian and joint-space actuators defined for my robot, and I want to dynamically load the desired actuators for my robot. `Element.attach` does not seem to provide the desired functionality, as it places the robot and actuators in separate namespaces. Is it possible to load both my actuators and robot from XMLs into the same namespace?