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
* @param parent
	 *            the parent element
	 * @throws ExtendsException
	 *             throws <code>ExtendsException</code> if the parent element
	 *             is <code>NOT_FOUND</code>,<code>WRONG_TYPE</code>,
	 *             <code>SELF_EXTEND</code>,<code>CIRCULAR</code>.
	 */
	public void checkExtends( DesignElement parent ) throws ExtendsException
	{
		String extendsName = getExtendsName( );
		IElementDefn defn = getDefn( );
		if ( parent == null )
		{
			throw new InvalidParentException( this, extendsName,
					InvalidParentException.DESIGN_EXCEPTION_PARENT_NOT_FOUND );
		}
		else if ( parent.getDefn( ) != defn )
		{
			throw new WrongTypeException( this, parent,
					WrongTypeException.DESIGN_EXCEPTION_WRONG_TYPE );
		}
		else if ( parent == this )
		{
			throw new CircularExtendsException( this, extendsName,
					CircularExtendsException.DESIGN_EXCEPTION_SELF_EXTEND );
		}
		else if ( parent.isKindOf( this ) )
		{
			throw new CircularExtendsException( this, parent,
					CircularExtendsException.DESIGN_EXCEPTION_CIRCULAR );