Different spaces for IK hands
When using arms in Inverse Kinematics mode, the target hand controllers are disconnected from the actual chain. These controllers are often children of a "root" controller, which is the topmost level in the hierarchy of bones. This is something animators often call the "world space".
The "world space" is good for various situations, such as when the character's hands need to be held still at one point while the rest of the body moves (imagine a circus acrobat holding himself in a rope, for instance), but we often need other "spaces". For example, animators should be able to rotate the character's Ribcage controller and have its IK hands to follow the movement. That would be the "Ribcage space", as many others which can be required by your animation.
How to do it...
Open the file
005-Spaces.blend. It has our character rig with enabled IK for both arms. Since the arms have a regular IK constraint, they are in the default "world space", with its controllers parented...
