This is another simple trick for the target expression. If you want to rotate multiple objects in one axe each.
Make a Null (called “proxy) targeting another Null (target). Drag the Proxy into the xpresso editor and connect the rotation ports separately to the individual objects you need to rotate.
This disco beamer is a simple example of the use of this trick. The beamer rotates around P to the target and the arm around H. Be careful to put the different elements as child of each other.