Text Kit: Upper case Math symbols in San Francisco

Question

In Introducing the new system fonts, the following screen shot was shown. Which UIFontDescriptorFeatureSettingsAttribute is used to enable this behaviour?

Answer 1

In case anyone else is struggling with this, here's the feature I found which will activate it:

let descriptor = UIFont.systemFontOfSize(24.0, weight: UIFontWeightLight).fontDescriptor()
let adjusted = descriptor.fontDescriptorByAddingAttributes(
    [
        UIFontDescriptorFeatureSettingsAttribute: [
            [
                UIFontFeatureTypeIdentifierKey: kCaseSensitiveLayoutType,
                UIFontFeatureSelectorIdentifierKey: kCaseSensitiveLayoutOnSelector
            ]
        ]
    ]
)
return UIFont(descriptor: adjusted, size: 24.0)