extensions/markdown-language-features/src/tableOfContents.ts/TableOfContents/createForNotebook
class TableOfContents:	public static async createForNotebook(parser: IMdParser, notebook: vscode.NotebookDocument): Promise<TableOfContents> {
		const entries: TocEntry[] = [];

		for (const cell of notebook.getCells()) {
			if (cell.kind === vscode.NotebookCellKind.Markup && isMarkdownFile(cell.document)) {
				entries.push(...(await this.buildToc(parser, cell.document)));
			}
		}

		return new TableOfContents(entries, parser.slugifier);
	}