Re: xkcd: LTR

From: Leif Halvard Silli <>
Date: Tue, 27 Nov 2012 17:26:19 +0100

Philippe Verdy, Tue, 27 Nov 2012 15:39:43 +0100:
> I've never said that user agents had to "'write" the prolog. It's the
> reverse: yes authors have to write a prolog (but the prolog is perfect here
> so this is not the fault of the author).

XML has (or more correctly: can have) a prolog. HTML does not have a
prolog. Now to the million dollar question: is your page in question
XML or HTML? Answer: Per the Content-Type, then it is HTML (that is:
"text/html"). Next question: Does the XML prolog have any effect when
the XML file (more specifically: the XHTML file) is served as HTML
(that is: "text/html")?

The answer is that, per HTML5, it does not have effect. And of course,
per HTML4, it does not have effect. As for XHTML 1, then it cannot
really regulate what is supposed to happen in text/html. The
problem/challenge, hover is that some Web browsers - such as W3m (a
text browser), Chrome, Opera and Safari - *do* look at the prolog for
encoding info *also* when served as HTML. But Firefox and Internet
Explorer do not. Which is according the HTML5 specification.

My guess is that it will *never* become conforming to use the XML
prologue in HTML files. However, that does not necessarily prevent
Firefox from looking at the prologue for encoding info, when *that* is
the only source of encoding info. In fact, I think the HTML5 encoding
sniffing algorithm already permits this (since it it has a step which
roughly says "if the user agent have other sources of information".)

So, for what it is worth - and with reference to your pages, I filed a
bug against Firefox, to make it start to use the encoding declartion of
the XML prologue, when nothing else is available:

leif halvard silli
Received on Tue Nov 27 2012 - 11:54:14 CST

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