---
title: identifier
framework: avfoundation
role: symbol
role_heading: Instance Property
path: avfoundation/avcaptionregion/identifier
---

# identifier

A string that identifies the region.

## Declaration

```swift
var identifier: String? { get }
```

## Discussion

Discussion The system considers two regions the same if their region identifier is equal. Your app needs to ensure that equal caption regions have the same property values. If this value is nil, the system instead treats two regions equal if their position and endPosition are the same. Captions referring to these regions belong to the same region when the system serializes them to a format like TTML.