Grid layout accepts a number of a columns, and then a comma separated list of entities. The entities will be placed in a grid with the given number of columns, in the order that they appear in the list.
If you put the symbol * (asterisk) instead of an entity name, that grid cell will be skipped.
You can also declare packages with the GridLayout (regardless of the type of diagram). After the layout arguments, specify one or more packages in the form: