Replace most of the "link extensions" section with a non-normative no…

…te (#109)

* Only use double-quotes in header examples
* Replace most of "link extensions" section to a non-normative note
* Remove references to request initiator and type

index.html

@@ -74,8 +74,7 @@ <h2>
         are defined in [[!DOM]].
       </p>
       <p>
-        The terms <dfn data-cite="FETCH#concept-request-destination">request destination</dfn>, <dfn data-cite="FETCH#concept-request-initiator">request initiator</dfn> and <dfn data-cite="FETCH#concept-request-type">request type</dfn>
-        are defined in [[!FETCH]].
+        The term <dfn data-cite="FETCH#concept-request-destination">request destination</dfn> is defined in [[!FETCH]].
       </p>
       <p>
         The terms <dfn data-cite="MIMESNIFF#parsable-mime-type">parsable MIME type</dfn> and <dfn data-cite="MIMESNIFF#supported-by-the-user-agent">unsupported MIME type</dfn> are defined in [[!MIMESNIFF]].
@@ -242,13 +241,11 @@ <h2>Processing</h2>
       link and a later fetch requesting the same resource.</p>
     </section>
     <section>
-      <h2>`link` element extensions</h2>
-      <p>[[!HTML]] defines the `as` content and IDL attributes. The state of
-      the `as` content attribute is taken into account in the above processing
-      model, which will set the <a>request destination</a> as well as the
-      corresponding <a>request type</a> and <a>request initiator</a>. This is necessary
-      to guarantee correct prioritization, request matching, application of the
-      correct [[!CSP3]] policy, and setting of the appropriate `Accept` request
+      <h2>`as` attribute</h2>
+      <p class=note>[[!HTML]] [defines](https://html.spec.whatwg.org/#attr-link-as) the
+      `as` content and IDL attributes. The attribute is necessary to guarantee
+      correct prioritization, request matching, application of the correct
+      [[CSP3]] policy, and setting of the appropriate `Accept` request
       header.</p>
       <p>When the resource is declared via the `Link` header field
       ([[!RFC5988]]), the resource's `as` attribute is defined via the `as`