public IMarker createMarker(IResource res, int line) throws CoreException {
      IMarker marker = null;
      // note: you use the id that is defined in your plugin.xml
      if (res != null) {
         marker = res.createMarker("com.my.marker");
         marker.setAttribute(IMarker.SEVERITY, IMarker.SEVERITY_ERROR);
         marker.setAttribute(IMarker.CHAR_START, 0);
         marker.setAttribute(IMarker.CHAR_END, 2);
         marker.setAttribute(IMarker.LINE_NUMBER, 2);
         marker.setAttribute(IMarker.LOCATION, "Snake file");
         marker.setAttribute(IMarker.MESSAGE, "Syntax error");

         Annotation annotation = new Annotation("org.eclipse.ui.workbench.texteditor.error", false, "Hello World");
         getVerticalRuler().getModel().addAnnotation(annotation, new Position(0, 5));
         getVerticalRuler().update();
      return marker;
   }