Type Alias OpenExternalFn 

pub type OpenExternalFn = Rc<dyn Fn(&mut Window, &mut App)>;

Invoked from the load-failure pane’s “Open in system viewer” button, so the host can hand the file to the OS default app — the viewer itself stays host-agnostic (no process spawning). Set via PdfView::set_on_open_external; without it the pane shows no button.

Aliased Type

pub struct OpenExternalFn { /* private fields */ }