Question regarding root_link_state_w, body_link_state_w, and root_com_state_w

[kbkartik]

What's the difference between:

1. root_link_state_w and body_link_state_w
2. root_link_state_w and root_com_state_w

Also, when should we use each of them?

[RandomOakForest]

This may have been addressed in this discussion.