Our custom Vaadin application frame isn't a MDI. It's "web SDI" . We didn't show popup windows aka internal frames with work-screen content. We did embedd the content directly into the web page. But we changed the default implementation a little bit because it makes sense to show popup windows for modal work-screens. Modal frames are important for database applications. Such frames could be used for showing record details, for creating new records, ...

So it makes sense that our application frame supports such specific work-screens. And the good news is that we've support for this.

It could look like following screenshot:

It's a screenshot from one of our test applications. The feature isn't generally available yet, but it will be part of the next VisionX release.