Offline capable widgets

Hi all,

I have a question regarding the offline capabilities of widgets. The "Creating offline mobile apps with Mendix" presentation from July 29th 2016 from Mendix tells us that you can add a single statement to a widget to make it offline capable: 

But not all widgets are currently supported to have this function switched on. So my question is; how do I know if a certain widget is able to be Offline capable? 

For example the Document Viewer widget (https://appstore.home.mendix.com/link/app/12/).

Thanks in advance,

Ward Brink