metalsmith-headings-identifier/spec/fixture/src/context.html

A Metalsmith plugin to add an id + anchor to all headings on a page

<h1 id="heading-0">0 heading</h1>
<div class="to-link">
  <h2 id="heading-1">1 heading</h2>
  <h2 id="heading-2">2 heading</h2>
</div>
<div class="not-to-link">
  <h2 id="heading-3">3 heading</h2>
  <h2 id="heading-4">4 heading</h2>
</div>