Possible Duplicate:
Xcode 4.2 Warnings when dropping Nav Controller on Tab Bar in IB
Every time I create a UINavigationController with interface builder there will be a warning:
Attribute Unavailable: Defines Presentation Context is not available prior to Xcode 4.2.
I know I can just uncheck Defines context in Navigation Controller to avoid this warning
but I want to know
I am using Xcode 4.2 and working on ios5
why this warning would show up??
and what's different if I check or uncheck Defines Context??