这是我的 XKB 配置：
$ setxkbmap -print
xkb_keymap {
xkb_keycodes { include "evdev+aliases(qwerty)" };
xkb_types { include "complete" };
xkb_compat { include "complete" };
xkb_symbols { include "pc+gb(custom)+us:2+inet(evdev)" };
xkb_geometry { include "pc(pc105)" };
};
是什么意思us:2？