Bug 93400 LTK UI should provide official API for structural content in the preview page
org.eclipse.ltk.ui.refactoring/src/org/eclipse/ltk/internal/ui/refactoring/ChangeElement.java
public abstract int getActive();
	
	/**
	 * Returns the element the change node represents. The method may return 
	 * <code>null</code> if the change node isn't related to an element.
	 * 
	 * @return the element modified by this change node
	 */
	public abstract Object getModifiedElement();
	
	/**
	 * Returns the change element's children.
	 * 
	 * @return the change element's children.
	 */
	public abstract ChangeElement[] getChildren();
	
	/**
	 * Returns <code>true</code> if the change node has
	 * one of the given group categories. Otherwise
	 * <code>false</code> is returned.
	 *
	 * @param categories the group categories to check
	 * 
	 * @return whether the change node has one of the given 
	 *  group categories
	 */
	public abstract boolean hasOneGroupCategory(List categories);
	
}