Extract `limit` to a named variable - it's just a count for how many changes we will be displaying per Chapter/Commodity/Heading. Since this is based on `UNION`s it's fetching 10 from each, joining everything together, sorting by operation date and limiting again to 10.

Depth(not the best name?) is a bit more tricky. Participates in sorting, so if Commodity and 2 measures were created on 2nd of September in the feed we first display measures and then commodities, because measures are **smaller** entities so therefore probably got created after Commodity if you look from Commodity feed perspective (or at least I think it would be reasonable to display in such order).