How are HTTP Cache-Control no-cache field names delimited? - http-headers

Question

The syntax for the HTTP Cache-Control no-cache directive of a response allows a field-name argument.
RFC7234#5.2.2.2 says:
5.2.2.2. no-cache
Argument syntax:
#field-name
// ...
If the no-cache response directive specifies one or more field-names,
then a cache MAY use the response to satisfy a subsequent request,
subject to any other restrictions on caching.
// ...
The specs state that the no-cache directive may "specif[y] one or more field-names". RFC7230#3.2 defines a field-name as being a token.
What the spec doesn't seem to cover is how multiple field names are delimited/separated.
How are Cache-Control no-cache field names delimited/separated?
Example with no field name (most common usage)
Cache-Control: no-cache
Example with single field name (never personally seen it, technically valid)
Cache-Control: no-cache=foo
Multiple field names ?
Cache-Control: no-cache=foo,bar
Cache-Control: no-cache=foo,bar
Cache-Control: no-cache=foo, bar
Cache-Control: max-age=60, private, no-cache=foo, bar, min-age=30
Cache-Control: max-age=60, private, no-cache="foo, bar", min-age=30
To me, only the last above example (the double-quoted no-cache value) is unambiguous.
What is the correct form to use?
I ask as I need to correctly parse arbitrary Cache-Control header values.

Answer 1

RFC's BNF at RFC2616#14.9 goes:
"no-cache" [ "=" <"> 1#field-name <"> ] ; Section 14.9.1
RFC2616#2.1 explains the # rule is a list:
#rule  
      A construct "#" is defined, similar to "*", for defining lists of  
      elements. The full form is "#element" indicating at least  
       and at most  elements, each separated by one or more commas  
      (",") and OPTIONAL linear white space (LWS). This makes the usual  
      form of lists very easy; a rule such as  
         ( *LWS element *( *LWS "," *LWS element ))  
      can be shown as  
         1#element 
RFC2616#2.2 tells you <"> just means "
<"> = <US-ASCII double-quote mark (34)>
Therefore it would be `Cache-Control: max-age=60, private, no-cache="foo, bar", min-age=30`, as you did in your last one.