string.swift

import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .gray

        let textView = UITextView(frame: CGRect(x: 20.0, y: 30.0, width: 300.0, height: 400.0))
        textView.textColor = UIColor.blue
        textView.backgroundColor = .white
        view.addSubview(textView)
        self.view = view

        let str =  NSMutableAttributedString()
        var attributes  = [NSAttributedStringKey.font: UIFont.systemFont(ofSize: 22.0)]
        do {
            let primo = try NSMutableAttributedString(string: "<b>Ciao</b>", attributes: attributes)
            str.append(primo)
        }catch{
            //error
        }
        textView.attributedText = str
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()