Xcode: changing double clicking file behavior

In XCode 6, click "Preferences...", then "Navigation", then under "Double Click Navigation" select "Same as Click"

Ahh,

Found the answer. There is a button in the ToolBar of the editor window that says "Grouped" or "Ungrouped".

If it says "Grouped" then files open in the same window.

If it says "Ungrouped" then files open in new windows.

Found the answer here:

http://meandmarkpublishing.blogspot.com/2007/06/reducing-xcodes-window-clutter.html