# `GSLayer.topMetricsKey`

*Instance Property*

Layer-specific metrics key for the top side bearing.

## Declaration

```swift
var topMetricsKey: String? { get set }
```

```objc
@property (nonatomic, strong) NSString * topMetricsKey;
```

[See also `topMetricsKey` in the Python API](https://docu.glyphsapp.com/#GSLayer.topMetricsKey)

```python
pyobjc_instanceMethods.topMetricsKey() -> str
pyobjc_instanceMethods.setTopMetricsKey_(topMetricsKey: str)
```

## Discussion

When `nil`, the glyph-level metrics key can still apply.

## See Also

### Metrics Keys

- [`GSLayer.widthMetricsKey`](/Core/GlyphsCore/GSLayer/widthMetricsKey) — Layer-specific metrics key for the advance width.
- [`GSLayer.leftMetricsKey`](/Core/GlyphsCore/GSLayer/leftMetricsKey) — Layer-specific metrics key for the left side bearing.
- [`GSLayer.rightMetricsKey`](/Core/GlyphsCore/GSLayer/rightMetricsKey) — Layer-specific metrics key for the right side bearing.
- [`GSLayer.bottomMetricsKey`](/Core/GlyphsCore/GSLayer/bottomMetricsKey) — Layer-specific metrics key for the bottom side bearing.
- [`GSLayer.vertWidthMetricsKey`](/Core/GlyphsCore/GSLayer/vertWidthMetricsKey) — Layer-specific metrics key for the vertical advance width.
- [`GSLayer.vertOriginMetricsKey`](/Core/GlyphsCore/GSLayer/vertOriginMetricsKey) — Layer-specific metrics key for the vertical origin.
- [`GSLayer metricsKey:name:operator:value:oppositeSite:atHeight:master:`](/Core/GlyphsCore/GSLayer/metricsKey:name:operator:value:oppositeSite:atHeight:master:) — Parses a metrics key into its referenced glyph, operator, numeric value, opposite side, height, and master.