In Xcode's preferences, there's a "navigation" tab that has some options about new tabs vs new windows. Also, in the same way that you can double click on a file in the project navigator to automatically open it in a new tab, it looks like (at least most of the time), if you double-click on an option from the "open quickly" pane it will open in a new tab.
ShanBot
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution