extensions/markdown-language-features/server/src/workspace.ts/VsCodeClientWorkspace/getContainingDocument
class VsCodeClientWorkspace:	getContainingDocument(resource: URI): md.ContainingDocumentContext | undefined {
		if (resource.scheme === Schemes.notebookCell) {
			const nb = this.notebooks.findNotebookDocumentForCell(resource.toString());
			if (nb) {
				return {
					uri: URI.parse(nb.uri),
					children: nb.cells.map(cell => ({ uri: URI.parse(cell.document) })),
				};
			}
		}
		return undefined;
	}