RFC 6265, "HTTP State Management Mechanism", April 2011

Errata ID: 6093
Status: Reported
Type: Editorial
Publication Format(s) : TEXT
Reported By: Attila Gulyas
Date Reported: 2020-04-12

Section 3 says:

Origin servers SHOULD NOT fold multiple Set-Cookie header fields into a single header field.  The usual mechanism for folding HTTP headers fields (i.e., as defined in [RFC2616]) might change the semantics of the Set-Cookie header field because the %x2C (",") character is used by Set-Cookie in a way that conflicts with such folding.

It should say:

Origin servers SHOULD NOT combine multiple Set-Cookie header fields into a single header field.  The usual mechanism for combining HTTP headers fields (i.e., as defined in [RFC2616]) might change the semantics of the Set-Cookie header field because the %x2C (",") character is used by Set-Cookie in a way that conflicts with such actions.

Notes:

RFC 6265 currently uses the verb "folding" when it refers to combining multiple header fields into one, which is ambiguous in the context of the HTTP/1 specs (both by RFC2616 and RFC 7230) where "folding" consistently refers to line folding, and the verb "combine" is used to describe merging same headers. Having a light HTTP knowledge, I naively started looking up "folding" in the HTTP specs, and was immediately confused by the results, others will probably be as well (especially is English is not their native tongue).

Examples to prove this consistency:
+ RFC 2616, Section 4.2, Message Headers, but searching for the for the word "combine" will bring up special cases.
+ RFC 7230, Section 3.2.2, Field Order
+ RFC 2616, Section 2.2, Basic Rules
+ RFC 7230, Section 3.2.4, Field Parsing

Thank you!

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