It's in the context of a Roster, and for each "selection", which is type "model", it finds the "cost" (which is the base cost), then finds the costs of any sub-items, sums them together, and then outputs the result.
@Mad-Spy yes, yes Idid! I only could clog 2h in it, but I like it. It feels very genuine and a work of love... The devs nailed the AdMech spot on so far. Cant wait to get home and explore some more necron tombs!