title: What is the "module" package.json field for?
body: <p>I've seen some npm packages (<a href="https://github.com/vuejs/vue/blob/v2.2.2/package.json#L6" rel="noreferrer">vue for example</a>) have a <code>module</code> field in their package.json.</p>
  <p>But <a href="https://docs.npmjs.com/cli/v7/configuring-npm/package-json" rel="noreferrer"><code>module</code> is not included in the package.json documentation</a> - is this a convention of some kind? Is there documentation for this somewhere?</p>