in reply to Re^2: Difference between LWP::UserAgent and AnyEvent::HTTP
in thread Difference between LWP::UserAgent and AnyEvent::HTTP

I can't find any information on X-AcceptDeltaUpdates

IIRC, MIME (used both for Mail and for HTTP) allows to invent non-standard "experimental" headers by prefixing them with "X-". The other end should silently ignore all unknown experimental headers.

Alexander

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Re^4: Difference between LWP::UserAgent and AnyEvent::HTTP
by haukex (Archbishop) on Sep 06, 2021 at 18:58 UTC
    IIRC, MIME (used both for Mail and for HTTP) allows to invent non-standard "experimental" headers by prefixing them with "X-".

    Correct, though its use is now discouraged - from RFC7231 (emphasis mine):

    Authors of specifications defining new fields are advised to keep the name as short as practical and not to prefix the name with "X-" unless the header field will never be used on the Internet. (The "X-" prefix idiom has been extensively misused in practice; it was intended to only be used as a mechanism for avoiding name collisions inside proprietary software or intranet processing, since the prefix would ensure that private names never collide with a newly registered Internet name; see [BCP178] for further information).

    And the linked RFC6648 is dedicated to discussing the deprecation, with some interesting background in the appendicies.