src/vs/workbench/api/common/extHostNotebookDocument.ts/ExtHostNotebookDocument/acceptDocumentPropertiesChanged
class ExtHostNotebookDocument:	acceptDocumentPropertiesChanged(data: extHostProtocol.INotebookDocumentPropertiesChangeData) {
		if (data.metadata) {
			this._metadata = Object.freeze({ ...this._metadata, ...data.metadata });
		}
	}