title: Can CFBundleVersion contain letters, and if so, how are they compared?
body: <p>According to Apple docs, the "Build" number, (aka <code>CFBundleVersion</code>) should be a "two-period-separated list of positive integers, as in 1.2.3". (<a href="https://developer.apple.com/library/ios/documentation/IDEs/Conceptual/AppDistributionGuide/ConfiguringYourApp/ConfiguringYourApp.html#//apple_ref/doc/uid/TP40012582-CH28-SW18" rel="noreferrer">Source: App Distribution Guide</a>, section: Setting the Version Number and Build String) (<a href="https://developer.apple.com/library/ios/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html#//apple_ref/doc/uid/20001431-102364" rel="noreferrer">Another source: Info.plist reference</a>, section about  <code>CFBundleVersion</code>)</p>
  
  <p>But, many released apps have build numbers with letters in them, for example, my version of Xcode is "6D570".</p>
  
  <p>Apple docs also say that build numbers must increase for each binary you submit to the App Store. </p>
  
  <p>So my question: can <code>CFBundleVersion</code> have letters? If yes, where is this documented, and how are the strings compared?</p>