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Re: [cssom] serializing U+0000 NULL

From: Simon Pieters <simonp@opera.com>
Date: Tue, 24 Nov 2015 17:19:14 +0100
To: www-style@w3.org, "Richard Gibson" <richard.gibson@gmail.com>
Cc: "Glenn Adams" <glenn@skynav.com>, "Boris Zbarsky" <bzbarsky@mit.edu>
Message-ID: <op.x8l4ycljidj3kv@simons-mbp>
On Thu, 19 Nov 2015 14:58:31 +0100, Richard Gibson  
<richard.gibson@gmail.com> wrote:

> I'm adding a selector escape function to Sizzle (the selection library
> backing jQuery), and originally planned to match
> https://drafts.csswg.org/cssom/#the-css.escape()-method but ran into a  
> snag
> regarding U+0000 NULL [1]. The draft calls for throwing an
> InvalidCharacterError exception in §2.1, but that doesn't fit with our
> library. It doesn't seem to fit within CSS, either, though. \0 is a valid
> escape per CSS Syntax [2], although it is returned as U+FFFD REPLACEMENT
> CHARACTER, and all major browsers but one now respect it
> (e.g., jQuery("<div><span
> data-attr='&#xFFFD;'/></div>")[0].querySelector("[data-attr='\\0 ']")
> returns the span)—the holdout is Safari, in which [data-attr='\\0 '] is
> treated as valid but never matches anything.
>
> So I'm wondering if you'd be willing to escape NULL rather than throwing  
> an
> exception. And if not, perhaps you could shed some light on why the
> exception was added in the first place?
>
> A brief history of NULL:
> * 2010 dbaron includes NULL in proposed escaping language (presumably as
> "\0 "): https://lists.w3.org/Archives/Public/www-style/2010Feb/0162.html
> * 2011 CSSOM WD includes escaping NULL:
> http://www.w3.org/TR/2011/WD-cssom-20110712/#common-serializing-idioms
> * 2012 (not directly related) Tab suggests a codification in input
> preprocessing of replacement with U+FFFD REPLACEMENT CHARACTER:
> https://lists.w3.org/Archives/Public/www-style/2012Oct/0687.html
> * 2013 CSSOM WD introduces InvalidCharacterError exceptions for escaping
> NULL (rethrown by CSS.escape):
> http://www.w3.org/TR/2013/WD-cssom-20131205/#common-serializing-idioms
> * 2015 no change:  
> https://drafts.csswg.org/cssom/#common-serializing-idioms
>
> [1] https://github.com/jquery/sizzle/pull/364#discussion_r44619782
> [2]
> http://www.w3.org/TR/2014/CR-css-syntax-3-20140220/#consume-an-escaped-code-point0
> and http://www.w3.org/TR/2014/CR-css-syntax-3-20140220/#escaping

This was apparently changed in  
https://github.com/w3c/csswg-drafts/commit/d83fba15cef8e0afc5b826cab41fa36293fb4c2f  
(before CSS.escape existed).

I suppose Glenn changed it because \0 was not valid CSS 2.1, but I don't  
find any direct statement regarding CSSOM from that month's archive. A  
related email is  
https://lists.w3.org/Archives/Public/www-style/2012Oct/0646.html

I don't mind changing back to escaping U+0000 as \0, or maybe \uFFFD  
directly?

-- 
Simon Pieters
Opera Software
Received on Tuesday, 24 November 2015 16:19:48 UTC

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