https://gnome.pages.gitlab.gnome.org/gtkmm/classGtk_1_1LevelBar.html
gtkmm: Gtk::LevelBar Class Reference
gtkclassreference
https://gnome.pages.gitlab.gnome.org/gtk/gtk4/property.LevelBar.value.html
Gtk.LevelBar:value
Reference for property Gtk.LevelBar:value
gtkvalue