Expand the clone note

Author: domenic

fetch.bs

@@ -5566,9 +5566,6 @@ run these steps:
     "<code>error</code>", then set <var>httpFetchParams</var> to <var>fetchParams</var> and
     <var>httpRequest</var> to <var>request</var>.
 
-    <p class=note>If user prompts are possible, then we need to clone <var>request</var> because
-    the user agent might need to re-send <var>request</var>.
-
    <li>
     <p>Otherwise:
 
@@ -5588,6 +5585,12 @@ run these steps:
      <var>httpRequest</var>.
     </ol>
 
+    <p class=note>If user prompts or redirects are possible, then the user agent might need to
+    re-send the request with a new set of headers after the user answers the prompt or the redirect
+    location is determined. At that time, the original request body might have been partially sent
+    already, so we need to clone the request (including the body) beforehand so that we have a
+    spare copy available.
+
    <li>
     <p>Let <var>includeCredentials</var> be true if one of