in a short sentence, describe AlpineJS
AlpineJS is a small, reactive JavaScript library that makes it easy to add interactivity to your HTML.
<script src="//unpkg.com/alpinejs"></script>
<div x-data="{ open: false }">
<button @click="open = true">Expand</button>
<span x-show="open">
Content...
</span>
</div>