"The most conservative" conversion in GMT?

Question

Section 19.3 “Tolerant Applications” of HTTP 1.1 RFC (2616) discusses the issue of parsing dates from HTTP client applications:

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

Two questions:

• Does this mean that the server MUST convert a value other than GMT to GMT? Or does this mean that if (optionally) he wants to convert a date value other than GMT to GMT (rather than reject), then he MUST use the most conservative possible conversion?

• What is meant by “the most conservative transformation possible”?

Change Although this is an old question, I am still interested in finding out the answer if it has one.

Answer 1

Does this mean that the server MUST convert a value other than GMT to GMT? Or does this mean that if (optionally) he wants to convert a date other than GMT to GMT (rather than reject), then he MUST use the most conservative possible conversion?

This is really something more specific to the area under consideration than what is applied as a whole. There is a project Although all date formats are case sensitive, recipients MUST match case, day, week, and time zone names. An HTTP / 1.1 implementation MAY internally represent the parsed expiration date earlier than the correct value, but SHOULD NOT internally represent the parsed expiration date later than the correct value. All payments related to expiration MUST be performed in GMT. The local time zone MUST NOT affect the calculation or comparison of time or duration. The cache SHOULD consider dates with time zones other than "GMT" invalid.

What is meant by “the most conservative transformation possible”?

In this context, this does not seem to mean anything specifically, except when it comes across two results, choose the most “conservative” date based on the context of the date.

Given 2 dates that were fuzzy, in the context of the Last-modified header, “later” will be the most conservative. But in the context of the Expires header, the earlier of them is more conservative. Anything that requires significant guesswork should simply return an error response.