Attributes are kept with an @ prefix and repeated elements become arrays, so nothing is quietly lost on the way across.
This page loads no libraries at all — the work is done by the browser itself. Your file is read on your own machine and never sent anywhere — open your browser's network tab and watch while you use it.
They are kept as keys prefixed with @, so an id attribute becomes "@id".
The second one turns the value into an array, so a list of items stays a list.
Everything here is free and works the same way — in your browser.