Way to combine XML files in same namespace?

[atyshka]

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?

[yuvaltassa]

Do you know about actuator disabling?
Perhaps you can put all the actuators in your model and only enable the ones you need?

[atyshka]

Yeah, come to think of it that would work for this particular scenario.

But I could see more applications for such include functionality in mjcf, such as dynamically selecting whether to use meshes or geoms for collisions. You can see over in the menagerie repo how robot XMLs have patch files to work better with MJX and it would be nice to have a cleaner solution.You could do that by writing it all in python, or creating multiple variants of the XML, but having a hybrid approach could be desirable for combining the clean readability of XML with the flexibility afforded by mjcf python.

I think this could be done with MJSpec now in Mujoco 3 but it's unclear to me how that is intended to integrate with dm_control. Is the long-term plan to migrate dm_control mjcf to MJSpec or do they serve different purposes?