title: What is the second parameter of NSLocalizedString()?
body: <p>What is the <code>*comment</code> parameter in:</p>
  
  <pre><code>NSString *NSLocalizedString(NSString *key, NSString *comment)
  </code></pre>
  
  <p>If I do this:</p>
  
  <pre><code>NSLocalizedString(@"Hello_World_Key", @"Hello World")
  </code></pre>
  
  <p>and have two versions of a Localizable.strings (English and Spanish), does each need the entry:</p>
  
  <pre><code>English.lproj/Localization.strings: @"Hello_World_Key" = @"Hello World";
  
  Spanish.lproj/Localization.strings: @"Hello_World_Key" = @"Hola Mundo";
  </code></pre>
  
  <p>Isn't the English one redundant?</p>