Snap to the rail: drop a module near a free slot and it locks into place. Remove one and the gap closes automatically, so rows never end up with awkward holes.
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Built on real hardware widths: Hager, ABB, Schneider and Siemens modules take the same space here as on the physical rail, so a layout that fits on screen fits at home.
In a field distribution board with several fields the DIN rail continues behind the cover, between the fields and at both ends. A breaker can't go there, because nobody could reach its toggle. Terminals like HLAK or Phoenix terminal blocks fit there well and leave the fields free for the protective devices. How much space there is differs from manufacturer to manufacturer, so measure your own enclosure before you plan terminals there. The planner shows this space hatched in orange.