The grid keeps per-plane offsets (leftOffset, rightOffset, groundOffset). Each plane has a widget
(a diamond in its colour) that the Perspective Grid and Perspective Selection tools drag: plain
moves the plane, Shift moves the objects on it too, Alt copies them (perspective.plane.move).
Double-clicking a widget, or ui.perspectivePlane, opens the plane's options dialog (location; Do
Not Move / Move All Objects / Copy All Objects). Object › Perspective › Move Plane to Match Object
(perspective.plane.matchObject). New objects attach where the plane is. Grid edits leave
attached art in place as the reference app does; perspective.grid.set {reproject: true} moves it
with the grid.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>