src/vs/workbench/api/common/extHostNotebook.ts/ExtHostNotebookController/_createExtHostEditor
class ExtHostNotebookController:	private _createExtHostEditor(document: ExtHostNotebookDocument, editorId: string, data: INotebookEditorAddData) {

		if (this._editors.has(editorId)) {
			throw new Error(`editor with id ALREADY EXSIST: ${editorId}`);
		}

		const editor = new ExtHostNotebookEditor(
			editorId,
			this._notebookEditorsProxy,
			document,
			data.visibleRanges.map(typeConverters.NotebookRange.to),
			data.selections.map(typeConverters.NotebookRange.to),
			typeof data.viewColumn === 'number' ? typeConverters.ViewColumn.to(data.viewColumn) : undefined
		);

		this._editors.set(editorId, editor);
	}