ConstIt renders nothing where it is declared: each matching surface renders the layers as its own, on top
of its built-in ones, so they read that surface's pane, sheet and state. A layer declared on several
surfaces is mounted on each (and on each pane of a frozen sheet); its copies share state through
useSurfaceState, which spans all of a sheet's surfaces.
Layers of separate SheetLayers stack in declaration order, unless a layer sets zIndex.
Declares layers for a sheet's surfaces, as children of a sheet (or workbook) element: