This is the exclusive Rig features from ToolBox
PrebondJoints are joints that controll the bond state of other joints.
select a joint
Hit ‘Make preBind Joints’

Practical cases are multiple, one of them id the ability to move bonded state dynamically. Here the fact to have biped and quadruped position for the same puppet is done with preBindJoint

Used to read rotation in a valide format as rotation can’t always use as driver for driven keys.

Options are :
Constraint : add position constraint for the basre of the system
Absolute out : add an absolute driver (positive negative free)
angle out : add angle compliant driver, if you need to drive an angle
use custom Orient : orient the system in a custom way

Angle of the scapula can expressed by the position of the red cross, more reliable for drivers.