spacer_0;
A spacer_0, demonstrated in the following figure, is a spacer that normally has no width. However, it indicates a point in a tile group where you want space to be inserted, if the group has to be stretched during layout. If the spacer_0 tiles in a group are assigned a positive width, all of them are assigned an equal share of the spacing.
The spacer_0 tile is defined in the base.dcl file.