A subset is a folder inside the Layout Book. Subsets allow you to easily organize your layouts and to define numbering rules for them. When working in the Navigator or Organizer, you can place any Layout into a Subset simply by dragging and dropping it into place.
If you create a new layout in the Organizer palette when right-clicking the name of a subset, it will be placed automatically in this subset. A Subset folder is indicated by a folder icon with a small number 1.
Subsets are not required; you can place a Layout into the Layout book without placing it into a Subset. However, subsets are useful in organizing large-scale projects with multiple sets of documentation. When assigning IDs to Layouts, you can reflect the subset hierarchy as part of the Layout ID system, to make it easier to find the right Layout when needed.
When setting up the contents of a Publisher Set, you can add a shortcut to any Layout Book Subset: this means Publisher Set items are created which are linked to the Subset folder and to its contents. This means that any changes to the contents of the Subset in the Layout Book are also reflected in the contents of the Publisher Set.