title: Appearance proxies / UI_APPEARANCE_SELECTOR in Swift?
body: <p>The Apple documentation states:</p>
  
  <blockquote>
    <p>To participate in the appearance proxy API, tag your appearance
    property selectors in your header with UI_APPEARANCE_SELECTOR.</p>
  </blockquote>
  
  <p>In Objective-C one can annotate properties with <code>UI_APPEARANCE_SELECTOR</code> like this:</p>
  
  <pre><code>@property (nonatomic, strong) UIColor *foregroundColor UI_APPEARANCE_SELECTOR;
  </code></pre>
  
  <p><strong>How can I do the same in Swift?</strong></p>