# `GSAxis.isCanonical`

*Instance Property*

Whether the axis has a four letter axis tag. Axis with longer tags are used for HOI.

## Declaration

```swift
var isCanonical: Bool { get }
```

```objc
@property (nonatomic, readonly) BOOL isCanonical;
```

```python
isCanonical() -> bool
```

## Discussion

Note that `canonicalTag` might still be `nil` even when this property returns `YES` since `canonicalTag` only returns non-`nil` values that that are four-characters long **and** fulfils the other OpenType variation axis tag requirements. See [`GSAxis axisTagIsOpenTypeCompliant:`](/Core/GlyphsCore/GSAxis/axisTagIsOpenTypeCompliant:).