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
}
	/**
	 * Returns the container interface for this element if this element is a
	 * container. Derived classes that represent containers must override this.
	 * <p>
	 * Part of: Containment system.
	 * 
	 * @param slot
	 *            the slot ID to get
	 * @return The container interface, or null if this element is not a
	 *         container.
	 */
	public ContainerSlot getSlot( int slot )
	{
		return null;
	}
	/**
	 * Returns a list of user properties defined in this element and somewhere
	 * up the inheritance chain.
	 * 
	 * @return The list of user properties.
	 */
	public List getUserProperties( )
	{
		List props = new ArrayList( );
		DesignElement e = this;
		while ( e != null )
		{
			List prop = e.getLocalUserProperties( );
			if ( prop != null )