I created a new OS X application project in Xcode, and browsed through the files. I found the following file.
It is fun that this kind of writing is allowed in a major formal product like Xcode from Apple. Yeah, I do hope not nobody tested the software.
By the way I think I found a bug in the latest version of Xcode. Trying to add a custom run time attribute then click on the value, made Xcode crash two times.