Structure of the groups

The group structure is stored after the drawing objects. There are two parts:

• Part 1: Definition which drawing object belongs to which group
  For each group which has at least one drawing object as a direct member and not only other groups the following blank separated list is given: The number of the group followed by the sequence numbers of the drawing objects which are direct members. This list ends with a zero. The sequence number of a drawing object is given by the list of drawing objects.

  Each drawing object can be a direct member of only one group. A drawing object which is not member of a group is not listed.

  Part 1 is concluded with a zero.

• Part 2: Definition of the group hierarchy.
  This part is a blank separated list of pairs of numbers concluded with two zeros. Each pair gives a groupnumber and the number of the parent group. Groups which do not have a parent group are not listed.