We've covered the majority of Bootstrap in big steps by now. We haven't yet looked at the other 2 script imports, namely "Popper" and "jQuery", what are those?
If you follow the script resource link:
<script src="https://email@example.com/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
You will see this at the very top:
/* Copyright (C) Federico Zivolo 2019 Distributed under the MIT License (license terms are at http://opensource.org/licenses/MIT). */
I found this one which seems to be the one. It seems that it deals with tooltips and popovers and in this case, Bootstrap builds off of this functionality. These docs are for v2 though and I haven't used either v1 or v2 separately from Bootstrap, so I can't comment the usefulness of this framework. I'd suggest trying it out, maybe it's the best thing ever? Who knows?
It even has a separate library for UI stuff too! For free! Great!