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
*            does not extend any other element
	 */
	public void setExtendsName( String name )
	{
		setExtendsElement( null );
		name = StringUtil.trimString( name );
		if ( name == null )
			return;
		String namespace = StringUtil.extractNamespace( name );
		name = StringUtil.extractName( name );
		extendsRef = new ElementRefValue( namespace, name );
	}
	/**
	 * Validates this element and its contents.
	 * 
	 * @param module
	 *            the module
	 * @return the list of the errors found in validation, each of which is the
	 *         <code>SemanticException</code> object.
	 */
	public final List validateWithContents( Module module )
	{
		ElementDefn elementDefn = (ElementDefn) getDefn( );
		List validatorList = ValidationExecutor.getValidationNodes( this,
				elementDefn.getTriggerDefnSet( ), true );
		ValidationExecutor executor = module.getValidationExecutor( );
		errors = executor.perform( this, validatorList );
		List list = new ArrayList( errors );
		int count = getDefn( ).getSlotCount( );
		for ( int i = 0; i < count; i++ )