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 slot within the container element that holds this element.
	 * 
	 * @return the container's slot in which this element appears
	 */
	public int getContainerSlot( )
	{
		return containerSlotID;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.IPropertySet#getObjectDefn()
	 */
	public IObjectDefn getObjectDefn( )
	{
		return getDefn( );
	}
	/**
	 * Returns the value of an element reference property as an element. Returns
	 * null if either the property is unset, or the reference is unresolved.
	 * 
	 * @param module
	 *            the module
	 * @param propName
	 *            the name of the element reference property to get
	 * @return the element referenced by the property
	 */
	public DesignElement getReferenceProperty( Module module, String propName )
	{
		ElementRefValue ref = (ElementRefValue) getProperty( module, propName );