Ios 文本工具箱：旧金山大写的数学符号

在介绍新系统字体时，显示了以下屏幕截图。哪个UIFontDescriptorFeatureSettingsAttribute用于启用此行为

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如果其他人对此感到困扰，我发现的一个功能将激活它：

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)