Evidently, several people have received the following rejection letter from Apple:
The message from Apple was as follows:
Performance - 2.5.1
Your app uses or references the following non-public APIs:
The use of non-public APIs is not permitted on the App Store because it can lead to a poor user experience should these APIs change.
Please revise your app to remove any non-public APIs. If you have defined methods in your source code with the same names as the above-mentioned APIs, we suggest altering your method names so that they no longer collide with Apple's private APIs to avoid your application being flagged in future submissions.
Additionally, if you are using third party libraries, please update to the most recent version of those libraries. If you do not have access to the libraries' source, you may be able to search the compiled binary using the "strings" or "otool" command line tools. The "strings" tool can output a list of the methods that the library calls and "otool -ov" will output the Objective-C class structures and their defined methods. These tools can help you narrow down where the problematic code resides. You could also use the "nm" tool to verify if any third-party libraries are calling these APIs.
I believe the required changes are minimal: