get_keysym = function get_keysym(keysyms, location) {

        if (!keysyms)
            return null;

        return keysyms[location] || keysyms[0];
    }
Given an array of keysyms indexed by location, returns the keysym
for the given location, or the keysym for the standard location if
undefined.

@private
@param {Number[]} keysyms
    An array of keysyms, where the index of the keysym in the array is
    the location value.

@param {Number} location
    The location on the keyboard corresponding to the key pressed, as
    defined at: http://www.w3.org/TR/DOM-Level-3-Events/#events-KeyboardEvent