Joint's cyan donut connected with grey circle

[d-kleine]

After having created a joint, I was wondering what the cyan donut connected by a grey link to a grey circle in the viewport mean (when the joint is not selected)? Could someone please clarify what this visualization represents and what both are good for?

Also, I think it would be very helpful to have a built-in legend or reference guide for these kinds of icons and symbols in the GUI help/documentation, since their meaning is not always immediately obvious.

[vick-yu]

Please check whether this is covered in the Isaac Sim documentation here: https://docs.isaacsim.omniverse.nvidia.com/6.0.0/openusd_tuning_tutorials/tutorial_03_inspect_asset.html