# `GSFileExtensionForOutlineFormat`

*Function*

The file extension conventionally used for an outline format.

## Declaration

```swift
func GSFileExtensionForOutlineFormat(_ outlineFormat: GSOutlineFormat) -> String!
```

```objc
NSString *GSFileExtensionForOutlineFormat(GSOutlineFormat outlineFormat);
```

```python
GSFileExtensionForOutlineFormat(outlineFormat: GSOutlineFormat) -> str
```

## Discussion

An unknown outline format uses the `otf` extension.

## See Also

### Formats and Grid Settings

- [`GSNameForOutlineFormat`](/Core/GlyphsCore/GSNameForOutlineFormat) — The font format identifier corresponding to an outline format.
- [`GSIsMeaningfulGrid`](/Core/GlyphsCore/GSIsMeaningfulGrid) — Whether the grid enables coordinate rounding.
- [`GSIsUnitGridOrMore`](/Core/GlyphsCore/GSIsUnitGridOrMore) — Whether either effective grid interval is at least one unit.
- [`GSMakeGridSetting`](/Core/GlyphsCore/GSMakeGridSetting) — Grid settings with the same effective interval in both directions.
- [`GSMultiplicator`](/Core/GlyphsCore/GSMultiplicator)