Xcode 4 why do I see XML when clicking on MainStoryBoard.storyboard: seems like a bug

To fix the issue, right-click MainStoryboard.storyboard, then choose "Open as >" and then "Interface Builder - iOS Storyboard".

Make sure you are not using the source control editor, which shows you the changes for a given file. You can change this in the Toolbar at the top right.

Check this link in the section "Editor"

This worked for me using xcode 6