src/vs/workbench/contrib/notebook/browser/view/renderers/cellRenderer.ts/AbstractCellRenderer/setupCollapsedPart
class AbstractCellRenderer:	protected setupCollapsedPart(container: HTMLElement): { collapsedPart: HTMLElement, expandButton: HTMLElement; } {
		const collapsedPart = DOM.append(container, $('.cell.cell-collapsed-part', undefined, $('span.expandButton' + ThemeIcon.asCSSSelector(unfoldIcon))));
		const expandButton = collapsedPart.querySelector('.expandButton') as HTMLElement;
		const keybinding = this.keybindingService.lookupKeybinding(EXPAND_CELL_INPUT_COMMAND_ID);
		let title = localize('cellExpandButtonLabel', "Expand");
		if (keybinding) {
			title += ` (${keybinding.getLabel()})`;
		}

		collapsedPart.title = title;
		DOM.hide(collapsedPart);

		return { collapsedPart, expandButton };
	}