Bug 176450 Support link to CSS Feature(Model Part)
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/PropertyCommand.java
if ( extendedItem.isExtensionModelProperty( prop.getName( ) )
					|| extendedItem.isExtensionXMLProperty( prop.getName( ) ) )
			{
				IReportItem extElement = extendedItem.getExtendedElement( );
				assert extElement != null;
				extElement.checkProperty( prop.getName( ), value );
				extElement.setProperty( prop.getName( ), value );
				return;
			}
		}
		PropertyRecord record = new PropertyRecord( element, prop, value );
		record.setEventTarget( getEventTarget( prop ) );
		getActivityStack( ).execute( record );
	}
	/**
	 * Private method to validate the value of a property.
	 * 
	 * @param prop
	 *            definition of the property to validate
	 * @param value
	 *            the value to validate
	 * @return the value to store for the property
	 * @throws PropertyValueException
	 *             if the value is not valid
	 */
	private Object validateValue( ElementPropertyDefn prop, Object value )
			throws SemanticException
	{
		
		if ( value == null )