thanks for the reference. excerpt:
You represent other special keys with keysyms. A keysym is a keyword that denotes a special key on the
keyboard. Keysyms are always preceded by a forward slash (/). Valid keysyms are Up, Down, Left, Right, Home,
End, PgUp, PgDn, Return, Tab, BkSp, Space, Delete, Insert, F1 through F16, and Escape. For instance, to include
the Tab key as part of a key sequence, you use /Tab.