Shelf buttons are shortcuts to commands and set up quick actions to speed up common workflows.
Select a Shape or Shapes and then click the Duplicator icon. This will create a Duplicator and automatically add your Shape(s) as Input Shapes.
Add a Rig Control to the Composition.
Add an Animation Control to the Composition.
Add an Align Behaviour to the Composition and connect it to the Deformers of any selected Shapes.
Clicking this Shelf item will create a default Rubber Hose Limb (the same command as Animation > Create Rubber Hose Limb). If you have a Shape selected the Rubber Hose will be connected to the Deformers attribute.