REGION subblocks in QUILD block

The definition of the different regions should be given in REGION subblocks of QUILD. Although the program counts the number of regions itself, it should be regarded good practice to make sure that the NR_REGIONS keyword corresponds to the correct number of REGION subblocks.

QUILD
  NR_REGIONS 2
  REGION 1
    1-11
  SUBEND
  REGION 2
    12 14 13 15 16 17 19 18 22 21 20
  SUBEND
END

The order in which the atom numbers are given does not matter, and in order that the input is easier to make and read, shortcuts are introduced. For instance, the "1-11" shortcut corresponds to "1 2 3 4 5 6 7 8 9 10 11", etc. Unlike other multi-level approaches, there is no need to have a shell structure for the different regions. I.e., the regions can overlap, or be defined as given above for DNA.