HtmlタグでStringを装飾する方法

• htmlタグをStringで書いて
• そのStringをData変換
• NSMutableAttributedString(data:options:documentAttributes)で装飾する
• options に documentType.html を指定

let str = "<i>testText</i>"
let stringWithBaseFont = NSString(format:"<span style=\"font-family: '-apple-system', 'HelveticaNeue'; font-size: \(22)\">%@</span>" as NSString, str)

stringWithBaseFont.data(using: String.Encoding.unicode.rawValue, allowLossyConversion: true)!

if let attributedString = try? NSMutableAttributedString(
    data: stringWithBaseFont.data(using: String.Encoding.unicode.rawValue, allowLossyConversion: true)!,
    options: [.documentType: NSAttributedString.DocumentType.html, .characterEncoding: String.Encoding.utf8.rawValue],
    documentAttributes: nil) {
    attributedString.addAttribute(.foregroundColor, value: UIColor.red, range: NSRange(location: 0, length: attributedString.length))
}