Are user defined runtime attributes documented for iOS 5?-Collection of common programming errors

In the Identity Inspector of the interface editor in Xcode 4, there is a section titled “User Defined Runtime Attributes”

Setting values here appears to work fine for iOS 5 and later, but I can find no documentation for this. If I use this, am I risking rejection for use of undocumented behavior? Is there Apple documentation that I am just unable to find?