Bug 138562 Splite extendsexcpetion to seperate sub class
The suggestion is Parent invalid Cycle extends Different type extends Not top level extends
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/parser/ReportElementState.java
SlotDefn slotInfo = (SlotDefn) containerDefn.getSlot( slotID );
		assert slotInfo != null;
		assert slotInfo.canContain( content );
		
		
		if ( container.getExtendsElement( ) != null )
		{
			handler
					.getErrorHandler( )
					.semanticWarning(
							new ContentException(
									container,
									slotID,
									content,
									ContentException.DESIGN_EXCEPTION_STRUCTURE_CHANGE_FORBIDDEN ) );
			return false;
		}
		
		if ( !slotInfo.isMultipleCardinality( )
				&& container.getSlot( slotID ).getCount( ) > 0 )
		{
			handler.getErrorHandler( ).semanticError(
					new ContentException( container, slotID,
							ContentException.DESIGN_EXCEPTION_SLOT_IS_FULL ) );
			return false;
		}
		
		
		addToNamespace( content );
		Module module = handler.getModule( );