Bug 183918 get relative file path of linkage library
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/ComplexPropertyCommand.java
* Check to see whether the reference points to a list.
	 * 
	 * @param ref
	 *            reference to the list into which to add the structure
	 * @throws PropertyValueException
	 *             if the <code>ref</code> doesn't refer a list property or
	 *             member.
	 */
	protected void checkListMemberRef( MemberRef ref )
			throws PropertyValueException
	{
		if ( !ref.isListRef( ) )
			throw new PropertyValueException( element, ref.getPropDefn( ),
					null, PropertyValueException.DESIGN_EXCEPTION_NOT_LIST_TYPE );
	}
	/**
	 * Check operation is allowed or not. Now if element is css style instance ,
	 * forbidden its operation.
	 * 
	 */
	private void checkAllowedOperation( )
	{
		if ( element != null && element instanceof CssStyle )
		{
			throw new IllegalOperationException(
					CssException.DESIGN_EXCEPTION_READONLY );
		}
	}
}