When the viewer pane is enabled you can switch to full screen with the full screen button. But while in full screen mode, if you toggle full screen back, a seperate viewer is opened and not switched back to the viewer pane.
Also the context menue says 'enter' toggles full screen mode, but in some viewers 'enter' does nothing and in some find bar is opened.
Another one: if nfo-viewer is used in viewer pane, the full screen button works, when nfo as seperate viewer the button doesn't work.
The viewer pane's "full screen" button really means "open a new full screen viewer", since the viewer pane is always attached to the lister.
Which ones? Some of the plugins have to pass Enter (and other keys) to the thing that's running inside the viewer (e.g. PDF and ActiveX). Maybe the Text plugin should handle Enter, but I expect it wasn't designed to be used full-screen. I couldn't find a plugin which opened the Find window when pressing Enter, BTW, but I did find a couple where Enter doesn't toggle fullscreen.
Looks like plugins need a way to tell Opus not to allow the full-screen option. The NFO viewer refuses the request to go fullscreen (on purpose) but doesn't have any way to disable the full-screen button. If the new viewer is started full-screen then it can't stop that, either.
I see!
It' the text viewer in hex mode.