in js/libs/ical.js [237:253]
var freebusyParam = function (name) {
return function(val, params, curr){
var fb = addFBType({}, params);
curr[name] = curr[name] || []
curr[name].push(fb);
storeParam(val, params, fb);
var parts = val.split('/');
['start', 'end'].forEach(function (name, index) {
dateParam(name)(parts[index], params, fb);
});
return curr;
}
}