Define sec-purpose in HTTP extensions

Author: noamr

fetch.bs

@@ -4103,7 +4103,7 @@ whose value must be a <a data-lt="structured header list">list</a>. Its ABNF is:
 Sec-Purpose    = sf-list
 </code></pre>
 
-It may contain a Item member which is the Token "prefetch". If so, this indicates the request’s
+It may contain an item member which is the token "prefetch". If so, this indicates the request’s
 purpose is to download a resource it is anticipated will be fetched shortly.
 
 <p class=note>This can be used, for example, to let the server adjust the caching expiry for