title: Multiple editor windows in Xcode
body: <p>When coding in Xcode, I double-click a file in the "Groups and files" list, and it opens a new editor window. I have several of these open at once.</p>
  
  <p>Until today.</p>
  
  <p>Today, when I double-click a file in the list, it opens the file in the last editor window I was using, meaning I can only have one editor window up at any one time.</p>
  
  <p>I guess I've switched some option somewhere by mistake. How do I get it back to the way I like it?</p>
  
  <p>I'm using Xcode 3.2.5</p>