In Inkscape, the cloning of a shape can be used to vary a parameter, such as the width of a shape, on multiple objects by just changing one object.

In order to figure out the tab shape for this project, a tab was constructed. It was cloned once to represent the width and height of a tab.

The tab is to be inserted into a slot. I made several slots. I made one and then copied that shape multiple times to the right of the first object. Each of those was cloned. Cloning will insure when one slot changes, the second will also change. The two slots top and bottom form a pair.

In this image you can see the paired slots, the original tab, and the tabs paired together. The original tab can be varied to change the shape of the other two tabs.

The next object was to put the two cloned objects together to form shapes which will be part of the shelving structures.