ReadonlycontextCore row/header builders + popover control (see the context type).
ReadonlygroupReadonlyoverflowOverflow tab-group ids.
ReadonlyoverflowOverflow panel ids in free (tab DOM) order.
ReadonlypinnedPinned panel ids whose tabs have clipped out of the strip, rendered in a dedicated "Pinned" section at the top of the dropdown, above the search box and MRU list. Empty unless the PinnedTabs module is active and the pinned block itself overflows.
The argument to IAdvancedOverflowService.renderOverflow.