extensions/markdown-language-features/src/languageFeatures/pathCompletions.ts/MdPathCompletionProvider/getFileUriOfTextDocument
class MdPathCompletionProvider:	private getFileUriOfTextDocument(document: SkinnyTextDocument) {
		if (document.uri.scheme === 'vscode-notebook-cell') {
			const notebook = vscode.workspace.notebookDocuments
				.find(notebook => notebook.getCells().some(cell => cell.document === document));

			if (notebook) {
				return notebook.uri;
			}
		}

		return document.uri;
	}