"Most Conservative"

[mnot@…]

Section 19.3 "Tolerant Applications" of the HTTP 1.1 RFC (2616) says on the subject of parsing dates from HTTP client applications:

If an HTTP header incorrectly carries a date value with a time zone other than GMT, it MUST be converted into GMT using the most conservative possible conversion.

Two questions:

Does this mean that the server MUST convert a non-GMT date value to GMT? Or does it mean that if (optionally) it chooses to convert a non-GMT date value to GMT (rather than rejecting it) then it MUST use the most conservative possible conversion?

What is meant by "the most conservative possible conversion"?

[mnot@…]

In p6, this is:

If an HTTP header field incorrectly carries a date value with a time zone other than GMT, it must be converted into GMT using the most conservative possible conversion.

​https://svn.tools.ietf.org/svn/wg/httpbis/draft-ietf-httpbis/latest/p6-cache.html#age.calculations

[mnot@…]

proposal: change to

Caches SHOULD consider dates with time zones other than "GMT" invalid.

[julian.reschke@…]

From [1814]:

fix description of handling invalid dates (see #375)

[fielding@…]

From [2082]:

Yet another attempt to explain HTTP-date, remove redundant requirements in sections that use HTTP-date, and correct some inconsistent requirements regarding time zones; related to #375 and [2077]