So that all applications which want to pick a file, will see the thunar dialog, instead of the foreign [GtkFileChooserDialog](https://developer.gnome.org/gtk3/stable/GtkFileChooserDialog.html). This dbus API seems to be used by [xdg-desktop-portal-gtk](https://github.com/flatpak/xdg-desktop-portal-gtk/) and [xdg-desktop-portal-kde](https://github.com/KDE/xdg-desktop-portal-kde), The reason to offer such a dialog/service in thunar would be, that the 'known stuff' could be used, no need to get used to the different ui/ux of GtkFileChooserDialog. I would not aim to support the full portal interface. Just this single service for now (Not a problem for thunar, since it anyhow runs as daemon) Implementation: The main thing to consider is, that existing widgets should be re-used as much as possible.Probably ThunarWindow could be extended/used as parent widget to inherit from. Or possible we need a abstract base-class and ThunarFileChooserDialog and ThunarWIndow inherit from that. For more info, check the https://gitlab.freedesktop.org/xdg/xdg-specs/-/issues/64