@post-list.html

<template>
<script>
const posts = (pages, under) =>
  pages.filter((page) => page.path.startsWith(under) && page.path !== under);
</script>
<ul>${posts(pages, attrs.under).map((post) => html`<li><a href="${post.path}">${post.title}</a></li>`)}</ul>
</template>