title: Eclipse 4 RCP Editor using SourceViewer Undo and Redo operations are not working
body: <p>I'm creating an editor using 'SourceViewer'. Given below is the code snippet from my '@PostConstruct' method.</p>
  
  <pre><code>// viewer is my SourceViewer instance   
  viewer = new SourceViewer(parent,verticalRuler, styles);
  
       IUndoManager undoManager = new TextViewerUndoManager(25);
       undoManager.connect(viewer);
       viewer.setUndoManager(undoManager);
  </code></pre>
  
  <p>Even though a default 'TextViewerUndoManager' associated  with 'SourceViewer'. Ctrl+Z and Ctrl+Y is not working.</p>
  
  <p>Another alternative that I tried is to override the 'IUndoManager getUndoManager(ISourceViewer sourceViewer)' of 'SourceViewerConfiguration' subclass and return a 'TextViewerUndoManager'. This approach also doesn't give the desired result.</p>
  
  <p>Kindly let me know what I'm missing in the above approaches.</p>