Can HTML imports be specified using the Link HTTP header, or only with a <link> tag?
<p>The HTML <code>&lt;link&gt;</code> element is most frequently used to include CSS stylesheets in a document. A typical use might look like this:</p>
<pre class="lang-html prettyprint-override"><code>&lt;link rel=&quot;stylesheet&quot; href=&quot;/style.css&quot; /&gt;
</code></pre>
<p>As an alternative to including the tag in the response body, it's possible for the server to specify the stylesheet using the <code>Link</code> HTTP header instead:</p>
<pre class="lang-none prettyprint-override"><code>HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Link: &lt;/style.css&gt;; rel=stylesheet

&lt;!doctype html&gt;
&lt;html&gt;
  &lt;head&gt;&lt;title&gt;Example&lt;/title&gt;&lt;/head&gt;
  &lt;body&gt;Hello!&lt;/body&gt;
&lt;/html&gt;
</code></pre>
<p>The proposed HTML Imports feature specification (<a href="https://www.w3.org/TR/html-imports/" rel="nofollow noreferrer">WC3 working draft</a>) adds a significant new feature to the <code>&lt;link&gt;</code> element: the ability to import all of the resources from another HTML document at once, potentially including multiple scripts, styles, and templates. A typical use may look like this:</p>
<pre class="lang-html prettyprint-override"><code>&lt;link rel=&quot;import&quot; href=&quot;/components.html&quot; /&gt;
</code></pre>
<p>My expectation was that it would also be possible to specify HTML imports using the <code>Link</code> header in the same way as styles, for cases like this:</p>
<pre class="lang-none prettyprint-override"><code>HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Link: &lt;/components.html&gt;; rel=import

&lt;!doctype html&gt;
&lt;html&gt;
  &lt;head&gt;&lt;title&gt;Example&lt;/title&gt;&lt;/head&gt;
  &lt;body&gt;&lt;ex-warm-welcome&gt;Hello!&lt;/ex-warm-welcome&gt;&lt;/body&gt;
&lt;/html&gt;
</code></pre>
<p>However, the working draft specification only explicitly mentions the <code>&lt;link&gt;</code> element; it doesn't make reference to the <code>Link</code> header. It also uses language that seems to require a <code>&lt;link&gt;</code> element to be associated with each import,</p>
<blockquote>
<p>Each document has an import link list, each of whose item is consist of link, the link element and location, a URL.</p>
</blockquote>
<p>I see that <code>&lt;link rel=&quot;import&quot; ... /&gt;</code> supports an <code>async</code> attribute that stylesheet links do not. It wouldn't be possible to specify this in the header, but given that it's an optional attribute I wouldn't expect this to prevent its support altogether.</p>
<p>Is it possible to specify an HTML import using the <code>Link</code> header, or not?</p>