The per-workbook workbook command scope this element owns (per GRID-BUFFERING-PLAN: each
WorkbookElement owns its own scope + undo manager for safe double-mount). Exposed so an
out-of-tree host — e.g. a hoisted task-pane area, which no longer renders inside this element's
scope — can bridge it via CommandScopeContext and resolve the workbook commands
(insertFunction / executeScript / undo / redo) against the SHOWN workbook.
null until the scope is created (or for a bare chromeless grid with no ambient command root).
Retrieve the sheet element associated with this workbook element.
null before the sheet has mounted.
Retrieve the viewport element associated with this workbook element.
null before the viewport has mounted.
Retrieve the workbook model associated with this workbook element.
For runtime type checking
Type returned via ref property