Bug 40788 [plan item] Configurable Next/Previous actions
Toolbar drop down, or editor specific control. Needs to be coordinated with Platform UI.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
return null;
	}
	/**
	 * Extracts the line differ from the displayed document's annotation model. If none can be found,
	 * a new differ is created and attached to the annotation model.
	 * 
	 * @return the linediffer, or <code>null</code> if none could be found or created.
	 * @since R3.0
	 */
	private DocumentLineDiffer getOrCreateDiffer() {
		IAnnotationModelExtension model= getModel();
		if (model == null)
			return null;
		DocumentLineDiffer differ= (DocumentLineDiffer)model.getAnnotationModel(IChangeRulerColumn.QUICK_DIFF_MODEL_ID);
		if (differ == null)
			differ= createDiffer(model);
		return differ;
	}
	/**
	 * Returns the <code>IChangeRulerColumn</code> of this editor, or <code>null</code> if there is none. Either
	 * the line number bar or a separate change ruler column can be returned.
	 * 
	 * @return an instance of <code>IChangeRulerColumn</code> or <code>null</code>.
	 * @since R3.0
	 */
	private IChangeRulerColumn getChangeColumn() {
		if (fChangeRulerColumn != null)
			return fChangeRulerColumn;
		else if (fLineNumberRulerColumn instanceof IChangeRulerColumn)
			return (IChangeRulerColumn) fLineNumberRulerColumn;