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/core/DesignElement.java
*            the container to set
	 * @param slot
	 *            the slot within the container where this element resides
	 */
	public void setContainer( DesignElement obj, int slot )
	{
		container = obj;
		containerSlotID = slot;
	}
	/**
	 * Gets the property data for either a system-defined or user-defined
	 * property.
	 * <p>
	 * Part of: Property system and user-defined property system
	 * 
	 * @param propName
	 *            The name of the property to lookup.
	 * @return The property definition, or null, if the property is undefined.
	 */
	public ElementPropertyDefn getPropertyDefn( String propName )
	{
		
		ElementPropertyDefn prop = (ElementPropertyDefn) getDefn( )
				.getProperty( propName );
		if ( prop == null )
			prop = getUserPropertyDefn( propName );
		return prop;
	}
	/**
	 * Validates that the given property name is either a system-defined or