Back to identifiers after httpwg/http-extensions#629.

Author: mikewest

index.bs

@@ -80,14 +80,14 @@ A request generated by a <{picture}> element would result in a request containin
 HTTP request header:
 
 ```
-Sec-Metadata: destination="image", site="cross-site"
+Sec-Metadata: destination=image, site=cross-site
 ```
 
 A top-level navigation from `https://example.com` to `https://example.com/` caused by a user's click
 on an in-page link would result in a request containing the following HTTP request header:
 
 ```
-Sec-Metadata: cause="user-activated", destination="document", site="same-origin"
+Sec-Metadata: cause=user-activated, destination=document, site=same-origin
 ```
 
 Framework {#framework}
@@ -113,7 +113,7 @@ unknown members, and members whose value is invalid.
 
 [=Navigation requests=] will contain a dictionary member whose key is
 "<dfn dict-member for="Sec-Metadata">`cause`</dfn>", and whose value is an
-<a for="structured header" grammar>`string`</a>. Other kinds of requests will not contain a
+<a for="structured header" grammar>`identifier`</a>. Other kinds of requests will not contain a
 {{Sec-Metadata/cause}} member.
 
 Valid {{Sec-Metadata/cause}} values are `user-activated` and `forced`, representing whether or not
@@ -141,8 +141,8 @@ To <dfn abstract-op local-lt="get cause">obtain the `cause` value</dfn> for a [=
 
 All requests will contain a dictionary member whose key is
 "<dfn dict-member for="Sec-Metadata">`destination`</dfn>", and whose value is a
-<a for="structured header" grammar>`string`</a> representing the [=request=]'s
-[=request/destination=].
+<a for="structured header" grammar>`identifier`</a> representing the [=request=]'s
+[=request/destination=], or the empty <a for="structured header" grammar>`string`</a>.
 
 Valid {{Sec-Metadata/destination}} values include all valid [=request=] [=request/destination=]
 values (the empty string, "`audio`", "`audioworklet`", "`document`", "`embed`", "`font`",
@@ -152,6 +152,9 @@ values (the empty string, "`audio`", "`audioworklet`", "`document`", "`embed`",
 ISSUE(whatwg/fetch#755): Fetch currently does not define `nested-document`. It would be ideal if
 we could add it, as the `target` member doesn't seem to be web-compatible.
 
+ISSUE: Perhaps we should define a specific identifier for the empty string, rather than switching
+types from `identifier` to `string` for the empty destination?
+
 <div algorithm="get destination">
     To <dfn abstract-op local-lt="get destination">obtain the `destination` value</dfn> for a
     [=request=] (|r|), return |r|'s [=request/destination=]. 
@@ -175,7 +178,7 @@ Sec-Metadata: ..., destination="document", ...
 
 All requests will contain a dictionary member whose key is
 "<dfn dict-member for="Sec-Metadata">`site`</dfn>", and whose value is an
-<a for="structured header" grammar>`string`</a> representing the relationship between the
+<a for="structured header" grammar>`identifier`</a> representing the relationship between the
 [=request=]'s [=request/origin=] and the [=url/origins=] for the [=URLs=] in the [=request=]'s
 [=request/url list=].