Xcode: What is LastUpgradeCheck?

Question

I did a git diff and saw in Project.xcodeproj/project.pbxproj:

    attributes = {
            BuildIndependentTargetsInParallel = YES;
+           LastUpgradeCheck = 0420;
    };

What's LastUpgradeCheck? Maybe I accidentally opened up the project with Xcode 4.2?

Answer 1

I think this happens when Xcode asks you to "modernize settings", and you do it or decline it (take action).

I think it also happens on Xcode dot releases; do you have a team of people that use different versions of Xcode? Or maybe a Lion system with 4.1/4.2 and a Snow Leopard system with 3.2.6?