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# highlightsBy

A set of flags that indicate how the button highlights when it receives a mouse-down event (that is, when the button is pressed).

```
var highlightsBy: NSCell.StyleMask { get set }
```

## Discussion

The value of this property is the logical OR of one or more of flags described in the “Constants” section of [`NSCell`](/documentation/AppKit/NSCell).

If both `NSChangeGrayCellMask` and `NSChangeBackgroundCellMask` are specified, both are recorded, but the resulting behavior depends on the button cell’s image. If the button has no image, or if the image has no alpha (transparency) data, `NSChangeGrayCellMask` is used; if the image has alpha data, `NSChangeBackgroundCellMask` is used. This arrangement allows the color swap of the background to show through the image’s transparent pixels.

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