title: Replace substring of NSAttributedString with another NSAttributedString
body: <p>I want to replace a substring (e.g. <code>@"replace"</code>) of an <code>NSAttributedString</code> with another <code>NSAttributedString</code>.</p>
  
  <p>I am looking for an equivalent method to <code>NSString</code>'s <a href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html#//apple_ref/doc/uid/20000154-SW6"><code>stringByReplacingOccurrencesOfString:withString:</code></a> for <code>NSAttributedString</code>.</p>