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/DefaultChangeElement.java
if (fChange instanceof TextEditBasedChange) {
			return ((TextEditBasedChange)fChange).hasOneGroupCategory(categories);
		} else {
			ChangeElement[] children= getChildren();
			for (int i= 0; i < children.length; i++) {
				if (children[i].hasOneGroupCategory(categories))
					return true;
			}
			return false;
		}
	}
	
	/**
	 * Sets the children.
	 * 
	 * @param children the children of this node. Must not be <code>null</code>
	 */
	public void setChildren(ChangeElement[] children) {
		Assert.isNotNull(children);
		fChildren= children;
	}
	private int getDefaultChangeActive() {
		int result= fChange.isEnabled() ? ACTIVE : INACTIVE;
		if (fChildren != null) {
			for (int i= 0; i < fChildren.length; i++) {
				result= ACTIVATION_TABLE[fChildren[i].getActive()][result];
				if (result == PARTLY_ACTIVE)
					break;
			}
		}