It's posible to map shift + shift on vi?

Question

I'm trying to configure a key-mapping using shift+shift, is this posible ?

I have tried:

<S-S> But this maps shift + S
<S><S> and this that maps to unknown 

Answer 1

You cannot map to modifier keys (like Ctrl, Shift, Alt) alone; they can only be used in combination with other keys that represent printable characters (like <C-a> = Ctrl + A). That's mostly due to the fact that terminals do not send keypress events for modifier keys alone. There are unfortunately even limitations in those combinations (also in GVIM). Some key combinations, like Ctrl + non-alphabetic cannot be mapped, and Ctrl + letter vs. Ctrl + Shift + letter cannot be distinguished.