---
title: key
framework: TelephonyMessagingKit
role: symbol
role_heading: Instance Property
platforms: [iOS 26.0+]
path: telephonymessagingkit/mmspartcontent/mmscustomheader/key
---

# key

The key for the custom header.

## Declaration

```swift
let key: String
```

## See Also

### Accessing header properties

- [value](telephonymessagingkit/mmspartcontent/mmscustomheader/value.md)