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

I've run into this issue, but it was a bit different. I had a merge issue with Git on my storyboard, so I had to manually edit the XML to resolve the conflict. After this, there was no 'Interface Builder-iOS Storyboard' option available in the "Open as" menu so I couldn't change it back to the visual editor. To fix this I simply restarted XCode and everything went back to normal.