* Eclipse class AnnotationPainter (in org.eclipse.jface.text.source; to be 
     found in org.eclipse.jface.text_*.jar):
      * paints decorations (provided by an annotation model)
      * can be configured with drawing strategies (public interface 
        AnnotationPainter.IDrawingStrategy)
   * The AnnotationPainter object is controlled by an object of class 
     SourceViewerDecorationSupport (in org.eclipse.ui.texteditor; to be found 
     in org.eclipse.ui.workbench.texteditor_*.jar)
      * has a protected method that creates a the AnnotationPainter object and 
        provides it with various drawing strategies (createAnnotationPainter())
         * there is even a reference to a feature request: "Could provide an 
           extension point for drawing strategies, see
           https://bugs.eclipse.org/bugs/show_bug.cgi?id=51498"
         * but: this bug entry was created in 2004 and never really modified 
           since
   * But: the method createAnnotationPainter() is protected and not final. 
     Hence, it could be overridden by a subclass. So the question is:
      * How to provide Eclipse with a modified SourceViewerDecorationSupport?
   * The class AbstractDecoratedTextEditor (in org.eclipse.ui.texteditor; to be
     found in org.eclipse.ui.editors_*.jar; also see type hierachy below) has
     protected, non-final field "fSourceViewerDecorationSupport" that is 
     accessed by get- and configureSourceViewerDecorationSupport() (both 
     protected and non-final)
 
 EditorPart (A)
 +- AbstractTextEditor (A)
    +- StatusTextEditor
       +- AbstractDecoratedTextEditor (A)
          +- JavaEditor (A)
          | |- ClassFileEditor
          | +- CompilationUnitEditor
          +- TextEditor
          
   * Possible approaches (at least the following three):
      * Start an Eclipse in Debug Mode to see the classes working in order to 
        find a point to hook in.
      * Look for open source Eclipse plugins that make use of custom annotations
        and find out how they did it.
         * Maybe Vrapper (https://github.com/vrapper/vrapper) is a good 
           candidate: It provides Vim-like commands for Eclipse. Example: To 
           delete the current line in Vim (in "normal mode"), you simply type 
           "dd". Vrapper also provides this shortcut -- and to denote the 
           special state after the first "d" it cuts the blinking cursor in 
           half. This does not look like a normal annotation.
      * Consult the community.