With version 5, elementaryOS introduced a picture-in-picture feature, allowing one to select any screen area and confine it to a floating rectangle above other windows. (Demoed here)
Is it possible to get this feature in Ubuntu?
EDIT: Just to further specify: I'm not looking for a full-screen window or a separate workspace in a picture-in-picture. What I'm looking for is elementaryOS's implementation of picture-in-picture, which allows picking any area within a window.