src/vs/workbench/contrib/notebook/common/model/notebookTextModel.ts/NotebookTextModel/_generateAlternativeId
class NotebookTextModel:	private _generateAlternativeId() {
		return `${this._notebookSpecificAlternativeId}_` + this.cells.map(cell => cell.handle + ',' + cell.alternativeId).join(';');
	}