ABNF recipient list production #element does not allow null element prior to first element

[reschke]

See https://www.rfc-editor.org/errata/eid5257.

Mailing list discussion starts here: https://lists.w3.org/Archives/Public/ietf-http-wg/2018JanMar/0131.html

[reschke]

See also #14

[reschke]

A simple fix for this would be to simplify the list expansion to just map \#element, and to put all other constraints in prose (the current approach doesn't work anyway due to the rules for empty list elements which are not counted).

[reschke]

Proposal for recipient list rule mapping:

#element => *( OWS "," ) *( [ OWS element ] OWS "," )

More eyes requested :-) @royfielding @mnot

[reschke]

The current proposal is incorrect as it does not allow a singleton element.

[reschke]

Maybe:

#element => *( "," OWS ) [ element ] *( OWS "," [ OWS element ] ) *( OWS "," )

better...

#element => [ element ] *( OWS "," [ OWS element ] )

for readability:

#element => [ element ] *( OWS "," OWS [ element ] )

[reschke]

PR updated

[royfielding]

And maybe

1#element => element *( OWS "," OWS [ element ] )

right?

[annevk]

@royfielding that'd outlaw Multiple-Element-Header: , somevalue, which seems wrongish?