# `GSFont setUserData:forKey:`

*Instance Method*

Sets user data for a key.

## Declaration

```swift
func setUserData(_ value: Any?, forKey key: String)
```

```objc
- (void) setUserData:(id) value forKey:(NSString *) key;
```

```python
setUserData_forKey_(value: object, key: str)
```

## Discussion

Pass `nil` as the value to remove existing user data for the key. This registers undo and marks the document as changed.

## See Also

### User Data

- [`GSFont.userData`](/Core/GlyphsCore/GSFont/userData)
- [`GSFont userDataForKey:`](/Core/GlyphsCore/GSFont/userDataForKey:) — Returns user data for a key, or `nil` if no value is set.
- [`GSFont removeUserDataForKey:`](/Core/GlyphsCore/GSFont/removeUserDataForKey:) — Removes user data for a key.