Vdom_keyboard.Keyboard_eventSourcematch_modifiers evaluates a t's modifiers vs the function's arguments. If an argument is not specified then that modifier is not evaluated.
val map :
t ->
f:
(([ `Ctrl of bool ]
* [ `Alt of bool ]
* [ `Shift of bool ]
* [ `Meta of bool ]
* Keyboard_code.t) ->
'a) ->
'a