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Info.plistis embedded in your application package and controls a number of things about your application. The display name shown in the Finder is listed here, as well as the bundle identifier which uniquely identifies the application. For more detailed information, see: Apple's documentation on Info.plist.
The bundle name (CFBundleName) is a name for the bundle, we also use it as executable name. It's shown below the app's icon in Finder as well as in app's menu bar, so should not be too long, ideally not longer than 16 characters. Also, it should not contain slash (/) nor colon (:) characters.
The CFBundleIdentifier identifies the application bundle. It should only contain characters in the following sets: alphanumeric (A-Z, a-z, 0-9), hyphen (-), and period (.). If you intend to submit your UDK application to the Mac App Store, what you enter here must match the identifier you set in Developer Certificate Utility when creating App ID.
If you need to modify or add a key to Info.plist that isn't exposed by this dialog, the overrides file can be edited by hand. It is a UTF-8 encoded XML document. Any keys in this file will override existing settings, so do not add a key to this file unless you know you need to modify it and understand the risks.