ROS2 humble JointTrajectoryPoint.msg documentation: what does this notation mean?

edit

You probably want an effort_controllers/JointGroupEffortController here if you want to command joint efforts directly without specifying position targets.

See here for more:

https://answers.ros.org/question/3682...

I believe joint trajectory controllers always try to hit a sequence of joint positions, and the effort_controllers version does so by sending effort commands based on the position errors.

I guess that you can also request that it attempt to correct the effort error as well, so you can hit target efforts at the same time you hit your target positions.

The bracket notation is telling you what you can optionally specify. You don't need to provide a target effort, but you may if you wish and I think in principle it will try to hit both.

I'd have to dig into code to understand how it works but I don't think you want the joint trajectory controller anyway.