src/vs/workbench/contrib/notebook/browser/notebookEditorWidget.ts/NotebookEditorWidget/updateSelectedMarkdownPreviews
class NotebookEditorWidget:	private async updateSelectedMarkdownPreviews(): Promise<void> {
		if (!this.useRenderer || !this._webview) {
			return;
		}

		if (!this._webview.isResolved()) {
			await this._resolveWebview();
		}

		const selectedCells = this.getSelectionViewModels().map(cell => cell.id);

		// Only show selection when there is more than 1 cell selected
		await this._webview?.updateMarkupPreviewSelections(selectedCells.length > 1 ? selectedCells : []);
	}