 
     func placeholderImage(for attachment: NSTextAttachment) -> UIImage {
         let imageSize = CGSize(width:64, height:64)
-        let placeholderImage: UIImage
+        var placeholderImage: UIImage
         switch attachment {
         case _ as ImageAttachment:
             placeholderImage = Gridicon.iconOfType(.image, withSize: imageSize)


extension EditorDemoController {

    struct Constants {
        static let defaultContentFont   = UIFont.systemFont(ofSize: 14)
        static let defaultHtmlFont      = UIFont.systemFont(ofSize: 24)
        static let defaultMissingImage  = Gridicon.iconOfType(.image)
        static let formatBarIconSize    = CGSize(width: 20.0, height: 20.0)
        static let headers              = [Header.HeaderType.none, .h1, .h2, .h3, .h4, .h5, .h6]
        static let lists                = [TextList.Style.unordered, .ordered]        

        default:
            placeholderImage = Gridicon.iconOfType(.attachment, withSize: imageSize)
        }
        if #available(iOS 13.0, *) {
            placeholderImage = placeholderImage.withTintColor(.label)
        }
        return placeholderImage
    }

