src/vs/workbench/api/common/extHostNotebookConcatDocument.ts/ExtHostNotebookConcatDocument/_init
class ExtHostNotebookConcatDocument:	private _init() {
		this._cells = [];
		this._cellUris = new ResourceMap();
		const cellLengths: number[] = [];
		const cellLineCounts: number[] = [];
		for (const cell of this._notebook.getCells()) {
			if (cell.kind === types.NotebookCellKind.Code && (!this._selector || score(this._selector, cell.document.uri, cell.document.languageId, true))) {
				this._cellUris.set(cell.document.uri, this._cells.length);
				this._cells.push(cell);
				cellLengths.push(cell.document.getText().length + 1);
				cellLineCounts.push(cell.document.lineCount);
			}
		}
		this._cellLengths = new PrefixSumComputer(new Uint32Array(cellLengths));
		this._cellLines = new PrefixSumComputer(new Uint32Array(cellLineCounts));
	}