src/vs/workbench/contrib/notebook/common/model/notebookTextModel.ts/NotebookTextModel/_overwriteAlternativeVersionId
class NotebookTextModel:	private _overwriteAlternativeVersionId(newAlternativeVersionId: string): void {
		this._alternativeVersionId = newAlternativeVersionId;
		this._notebookSpecificAlternativeId = Number(newAlternativeVersionId.substr(0, newAlternativeVersionId.indexOf('_')));
	}