Feature 114 (Phase 6): the logical size + current position of a virtualized collection (e.g. a DataGrid), reported to assistive technology INDEPENDENT of how many items are materialized. TotalItems is the total logical item count (from the collection's RowCount/ItemCount); FocusedIndex is the focused item's logical index within that total (None when nothing is focused). Both are computed from the logical model, never from the realized slice (FR-012).