If I use the NSXMLParserDelegate, will my application crash or be rejected if I target OS 3.1?

I am using the iPhone 4.0 SDK for my development and the NSXMLParserDelegate protocol in my code. I am plann开发者_StackOverflow中文版ing to make this work on 3.1 as well by making the deployment target 3.1 and base SDK 4.0.

Since NSXMLParserDelegate is only on 4.0 and above will it work on iPhone 3.1?

Even if it works will Apple reject the app?

No, you can use APIs from later versions of the OS in builds for older versions, so long as you properly handle running on the older OS. This code is safe.