Two macros are distributed. One, @bones_50A selects current main chain level Bone atoms (values 1 and 3) within 50Å. The other, @bones_20A, draws main chain and side chain levels within 20Å. This is the latter:
Bone_setup ano1 20a 20. 1 2 3 ; centre_id wait_id bone_draw
The skeleton is called ano1, the created object is called 20a.