Where:
- map_mol_no is an integer number
- coord_mol_no is an integer number
- invert_flag is an integer number
generate a new map that has been masked by some coordinates
(mask-map-by-molecule map-no mol-no invert?) creates and displays a masked map, cuts down density where the coordinates are (invert is 0). If invert? is 1, cut the density down where there are no atoms atoms.