//! A Mirror of bodies keeps the placement each body was picked at (`placements`: one occurrence
//! path per body), and mirrors the body where that placement shows it, so a body of a moved or
//! inserted component, or of one of its further instances, is mirrored where it is seen. Older
//! designs need no transformation: a Mirror without `placements` mirrors the bodies' own
//! geometry as before; the last release asks for an update instead of mirroring them there.