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RE: Postel's Law Has No Exceptions

• To: "Joshua Allen" <joshuaa@m...>,"Simon St.Laurent" <simonstl@s...>,<xml-dev@l...>
• Subject: RE: Postel's Law Has No Exceptions
• From: "Julian Reschke" <julian.reschke@g...>
• Date: Wed, 20 Aug 2003 01:02:02 +0200
• Importance: Normal
• In-reply-to: <4F4182C71C1FDD4BA0937A7EB7B8B4C10A567CA5@r...>

> From: Joshua Allen [mailto:joshuaa@m...]
> Sent: Wednesday, August 20, 2003 12:39 AM
> To: Simon St.Laurent; xml-dev@l...
> Subject: RE:  Postel's Law Has No Exceptions
>
>
> > > "The creators of XML were wrong. Postel's Law has no exceptions."
> >
> > Just to be clear, this is Aaron Swartz's argument, not mine.   I
> > disagree with Aaron, but for reasons that are not yet coherent enough
> to
> > post.  I figured his provocation was worth some thought, however.
>
> A fine permathread.  I often find myself defending Postel's law against
> those who feel that they have discovered an exception.
>
> I am not a fan of those who claim that XML design is a counterexample to
> Postel's law.  It's true that XML is not very liberal in what it
> accepts, but that is not the same as saying that it is OK to be liberal
> in what you send -- I think we risk implicitly endorsing "liberal
> senders" by heralding the death of Postel's law.  I know I have seen my
> fair share of people who think it is OK to send utter crap out on the
> wire since "it is the receiver's responsibility to catch the error --
> and stop mentioning Postel's law -- some pundit told me it doesn't apply
> to XML".

I think XML is a very good example that in some cases, to be conservative in
*both* what you send and what you accept makes more sense.

Speaking from server implementation experience: just because one popular
server chose to be "liberal" (in that case, non-compliant), implementors of
competing servers are now forced to implement that buggy behaviour as
well -- just because clients are relying on that behaviour. I don't think
this was what Jon Postel intended back then.

Julian

--
<green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760

• References:
  • RE: Postel's Law Has No Exceptions
    • From: "Joshua Allen" <joshuaa@m...>

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