docs: def parse_mixed_delim_str(line):
      """Turns .obj face index string line into [verts, texcoords, normals] numeric tuples."""
      arrs = [[], [], []]
      for group in line.split(' '):
          for col, coord in enumerate(group.split('/')):
              if coord:
                  arrs[col].append(int(coord))
  
      return [tuple(arr) for arr in arrs]