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
if ( base == null )
		{
			extendsRef = null;
		}
		else
		{
			
			assert base.getDefn( ) == getDefn( );
			
			assert base.getName( ) != null;
			String namespace = null;
			Module root = base.getRoot( );
			if ( root instanceof Library )
			{
				namespace = ( (Library) root ).getNamespace( );
			}
			extendsRef = new ElementRefValue( namespace, base );
			base.addDerived( this );
		}
	}
	/**
	 * Returns the data set element, if any, for this element.
	 * 
	 * @param module
	 *            the module of this element
	 * 
	 * @return the data set element defined on this specific element
	 */
	public TemplateParameterDefinition getTemplateParameterElement(
			Module module )