Use "bindsym" instead of "bind". You have to use the names of keys
as in xmodmap. To get a list of currently bounud symbols, use
xmodmap -pke
Technical quirk: Xlib generated MappingNotify events upon
XkbMapNotify events (from XKB, as the name says). XCB does not yet
have support for XKB, thus we need to select and handle the event
by ourself. Hopefully, this will change in the future.