title: Is there a way to install older iOS SDKs in Xcode?
body: <p>I'd like to ensure some backward compatibility for my apps by compiling them using the older SDKs to test for newer classes and methods.  However, Xcode is only available with SDKs for the latest iOS versions.</p>
  
  <p>I've downloaded and installed the iOS 3.1.3 SDK (<a href="http://0xced.blogspot.com/2010/07/using-sdk-313-with-iphone-sdk-4.html" rel="noreferrer">using the method described here</a>) and that works fine. My code is full (not so full :-) ) of __IPHONE_OS_VERSION_MAX_ALLOWED, __IPHONE_OS_VERSION_MIN_REQUIRED and such respondsToSelector.</p>
  
  <p>This works right now for the iOS 3.1.3 SDK, but what if in the future I wanted to repeat this process with the 4.0 SDK?  Is there a general process for installing older SDK versions in the latest Xcode?</p>