Clarify preload "as" processing

- The link options destination is always a "destination type".
- We only use the "preload" translating when preloading.
- An invalid "as" translates to an empty string, which would cancel the preload request down the line.
- The default remains the empty string, and rel=icon can set the request's destination manually to image as before.

Closes #11726.

Author: noamr

source

@@ -2742,6 +2742,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
        <li><dfn data-x="concept-request-traversable-for-user-prompts" data-x-href="https://fetch.spec.whatwg.org/#concept-request-window">traversable for user prompts</dfn></li>
        <li><dfn data-x-href="https://fetch.spec.whatwg.org/#request-top-level-navigation-initiator-origin">top-level navigation initiator origin</dfn></li>
        <li><dfn data-x-href="https://fetch.spec.whatwg.org/#concept-request-add-range-header">add a range header</dfn></li>
+       <li><dfn data-x-href="https://fetch.spec.whatwg.org/#destination-type">destination type</dfn></li>
       </ul>
      </li>
      <li>
@@ -16764,7 +16765,6 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
 
   <dl>
    <dt><dfn data-x="link options href">href</dfn> (default the empty string)</dt>
-   <dt><dfn data-x="link options destination">destination</dfn> (default the empty string)</dt>
    <dt><dfn data-x="link options initiator">initiator</dfn> (default "<code
    data-x="">link</code>")</dt>
    <dt><dfn data-x="link options integrity">integrity</dfn> (default the empty string)</dt>
@@ -16773,6 +16773,9 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
    string)</dt>
    <dd>A string</dd>
 
+   <dt><dfn data-x="link options destination">destination</dfn> (default the empty string)</dt>
+   <dd>A <span>destination type</span>.</dd>
+
    <dt><dfn data-x="link options crossorigin">crossorigin</dfn> (default <span
    data-x="attr-crossorigin-none">No CORS</span>)</dt>
    <dd>A <span>CORS settings attribute</span> state</dd>
@@ -16823,11 +16826,6 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
     <p>Let <var>options</var> be a new <span>link processing options</span> with</p>
 
     <dl class="props">
-     <dt><span data-x="link options destination">destination</span></dt>
-     <dd>the result of <span
-     data-x="translate a preload destination">translating</span> the state of <var>el</var>'s <code
-     data-x="attr-link-as">as</code> attribute</dd>
-
      <dt><span data-x="link options crossorigin">crossorigin</span></dt>
      <dd>the state of <var>el</var>'s <code data-x="attr-link-crossorigin">crossorigin</code>
      content attribute</dd>
@@ -16980,7 +16978,7 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
      </li>
 
      <li><p><span>Apply link options from parsed header attributes</span> to <var>options</var>
-     given <var>attribs</var>.</p></li>
+     given <var>attribs</var> and <var>rel</var>. If that returned false, then return.</p></li>
 
      <li><p>If <var>attribs</var>["<code data-x="attr-link-imagesrcset">imagesrcset</code>"] <span
      data-x="map exists">exists</span> and <var>attribs</var>["<code
@@ -17000,14 +16998,26 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
 
   <div algorithm>
   <p>To <dfn>apply link options from parsed header attributes</dfn> to a <span>link processing
-  options</span> <var>options</var> given <var>attribs</var>:</p>
+  options</span> <var>options</var> given <var>attribs</var> and a string <var>rel</var>:</p>
 
   <ol>
-   <li><p>If <var>attribs</var>["<code data-x="attr-link-as">as</code>"] <span data-x="map
-   exists">exists</span>, then set <var>options</var>'s <span data-x="link options
-   destination">destination</span> to the result of <span
-   data-x="translate a preload destination">translating</span> <var>attribs</var>["<code
-   data-x="attr-link-as">as</code>"].</p></li>
+   <li>
+    <p>If <var>rel</var> is "<code data-x="rel-preload">preload</code>":</p>
+
+    <ol>
+     <li><p>If <var>attribs</var>["<code data-x="attr-link-as">as</code>"] does not <span
+     data-x="map exists">exist</span>, then return false.</p></li>
+
+     <li><p>Let <var>destination</var> be the result of <span data-x="translate a preload
+     destination">translating</span> <var>attribs</var>["<code
+     data-x="attr-link-as">as</code>"].</p></li>
+
+     <li><p>If <var>destination</var> is null, then return false.</p></li>
+
+     <li><p>Set <var>options</var>'s <span data-x="link options destination">destination</span> to
+     <var>destination</var>.</p></li>
+    </ol>
+   </li>
 
    <li><p>If <var>attribs</var>["<code data-x="attr-link-crossorigin">crossorigin</code>"] <span
    data-x="map exists">exists</span> and is an <span>ASCII case-insensitive</span> match for one of
@@ -17039,6 +17049,8 @@ interface <dfn interface>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
    a <span>fetch priority attribute</span> keyword, then set <var>options</var>'s <span
    data-x="link options fetch priority">fetch priority</span> to that <span>fetch priority
    attribute</span> keyword.</p></li>
+
+   <li><p>Return true.</p></li>
   </ol>
   </div>
 
@@ -17190,7 +17202,7 @@ data-x="rel-preload">preload</span>; <span data-x="attr-link-as">as</span>=font<
      </li>
 
      <li><p><span>Apply link options from parsed header attributes</span> to <var>options</var>
-     given <var>attribs</var>.</p></li>
+     given <var>attribs</var> and <var>rel</var>. If that returned false, then return.</p></li>
 
      <li><p>Run the <span>process a link header</span> steps for <var>rel</var> given
      <var>options</var>.</p></li>
@@ -28989,7 +29001,7 @@ document.body.appendChild(wbr);</code></pre>
   <ol>
    <li><p>If <var>destination</var> is not "<code data-x="">fetch</code>", "<code data-x="">font</code>",
    "<code data-x="">image</code>", "<code data-x="">script</code>", "<code data-x="">style</code>",
-   or "<code data-x="">track</code>", then return null.</p></li>
+   or "<code data-x="">track</code>", then return nulll.</p></li>
 
    <li><p>Return the result of <span
    data-x="concept-potential-destination-translate">translating</span>
@@ -29112,6 +29124,15 @@ document.body.appendChild(wbr);</code></pre>
    data-x="create link options from element">creating link options</span> from
    <var>el</var>.</p></li>
 
+   <li><p>Let <var>destination</var> be the result of <span data-x="translate a preload
+   destination">translating</span> the keyword representing the state of <var>el</var>'s <code
+   data-x="attr-link-as">as</code> attribute.</p></li>
+
+   <li><p>If <var>destination</var> is null, then return.</p></li>
+
+   <li><p>Set <var>options</var>'s <span data-x="link options destination">destination</span> to
+   <var>destination</var>.</p></li>
+
    <li>
     <p><span>Preload</span> <var>options</var>, with the following steps given a <span
     data-x="concept-response">response</span> <var>response</var>: