in src/InMemoryProvider.ts [378:384]
private _getKeysForRange(data: Dictionary<ItemType[]> | Dictionary<ItemType>, keyLowRange: KeyType, keyHighRange: KeyType,
lowRangeExclusive?: boolean, highRangeExclusive?: boolean): string[] {
const keyLow = serializeKeyToString(keyLowRange, this._keyPath);
const keyHigh = serializeKeyToString(keyHighRange, this._keyPath);
return filter(keys(data), key =>
(key > keyLow || (key === keyLow && !lowRangeExclusive)) && (key < keyHigh || (key === keyHigh && !highRangeExclusive)));
}