Summary

The macro below splits a box shape measuring 100mm×50mm into four equal-sized smaller boxes measuring 25mm×50mm:

The example below creates one box 40mm×50mm and 3 boxes 20mm×50mm:

Percentage-size and proportional components can be used together:

The example below expands the box from the top left:

The example below sets the box size from the top left:

From these last examples it can be seen that if there are no proportional components then the overall size of the new box(es) can be different to the original box size.