Bug 151959 inappropriate screen operation
steps to reproduce: - create a report - add a grid item (3x3) - switch to Outline view - expand the grid item to see its rows and cells - select the grid item, and drag it into any of its own cell expected behavior: - is it an invalid screen operation? if it is, it should be banned actual behavior: - the grid item was disappeared surprisingly
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
protected ContainerSlot slots[] = null;
	/**
	 * Support for id inheritance. If it is set, base id must be larger than
	 * <code>0</code>.
	 */
	protected long baseId = NO_BASE_ID;
	/**
	 * Default constructor.
	 */
	public DesignElement( )
	{
		
	}
	/**
	 * Constructs the design element with the name.
	 * 
	 * @param theName
	 *            initial element name
	 */
	public DesignElement( String theName )
	{
		name = theName;
	}
	/**
	 * Registers a listener. A listener can be registered any number of times,
	 * but will receive each event only once.
	 * <p>
	 * Part of: Notification system.
	 * 
	 * @param obj