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Re: [CSS21][CSS3 Text] Re: Treating carriage return as white space in layout

From: Henri Sivonen <hsivonen@iki.fi>
Date: Tue, 3 Aug 2010 16:51:32 +0300
Cc: www-style@w3.org
Message-Id: <115B4679-9C33-4B3C-B75B-6B010921FF1F@iki.fi>
To: fantasai <fantasai.lists@inkedblade.net>
On Aug 2, 2010, at 23:23, fantasai wrote:

> On 07/08/2010 12:53 PM, Henri Sivonen wrote:
>> On Jul 7, 2010, at 14:27, fantasai wrote:
>> 
>>> CSS3 Text seems pretty clear to me:
>>>  # In the context of CSS, the document white space set is defined to be any
>>>  # space characters (Unicode value U+0020), tab characters (U+0009), or line
>>>  # break characters (defined by the document format: typically line feed,
>>>  # U+000A). Control characters besides the white space characters and the
>>>  # bidi formatting characters (U+202x) are treated as normal characters and
>>>  # rendered according to the same rules.
>> 
>> This part alone would be clear...
>> 
>>>  # The document parser must normalize line break character sequences according
>>>  # to its own format rules before CSS processing takes effect.
>> 
>> ...but this part steps outside the jurisdiction of CSS (or is at least a weird
>> use of 'must' to reinforce whatever 'its own format rules' say)...
> 
> I think it's reasonable for CSS to say whether CSS white space collapsing
> takes effect before or after non-CSS processing.

Fair enough.

>>> However, in
>>>  # generated content strings the line feed character (U+000A) and only the line
>>>  # feed character is considered a line break sequence. For CSS white space
>>>  # processing all line breaks must be normalized to a single character
>>>  # representation—usually the line feed character (U+000A)—here called a
>>>  # "line break".
>> 
>> ...and this part introduces doubt about whether the first paragraph was actually clear.
> 
> This part basically says what the equivalent of document-language normalization
> rules are for generated content. I don't see how this is inconsistent with
> the first paragraph.

I thought the last sentence had a scope broader than just generated content. It's not entirely clear what the scope of the last sentence is.

>>> According to CSS3 Text, carriage returns are not white space characters.
>>> They therefore do not get any special treatment during the white space
>>> collapsing process and are treated the same as any other non-whitespace
>>> control character.
>>> 
>>> Both CSS3 Text (quoted above) and CSS2.1 (section 16.6.3) say that carriage
>>> returns are treated as characters to render the same as normal characters:
>>> they do not behave as control characters. I assume this means that if
>>> there's a glyph in the font they are rendered as that glyph, otherwise some
>>> substitution process is triggered just as for missing glyphs of other
>>> characters. If that's not what we want for control characters, and what we
>>> want is for the character to definitely disappear, or to definitely fall
>>> back to nothing, then we'll need to adjust both specs to say so.
>> 
>> I think that's not what we want. I'm suggesting that CR be treated as whitespace.
> 
> "treated as whitespace" is vague. Different kinds of whitespace are treated
> differently.

My exact requirements are vague. I know that I need CR to behave in a whitespace-ish way, but I'm not confident about the details.

>>> The only thing I see missing in CSS3 Text is a statement that characters
>>> designated as line breaks cause forced line breaks, which is pretty obvious,
>>> but should be stated clearly somewhere. :)
>>> 
>>> Is the behavior specced in CSS3 Text what you want, and would backporting
>>> some changes to CSS2.1 to create the same effect solve the problem, or is
>>> there something else you needed here?
>> 
>> For white-space-collapse: collapse;, I need CR to collapse.
> 
> To collapse to what? Should it be treated as a space/tab or as a line break
> during collapsing? (In Latin these both collapse to space, but not in other
> scripts.)

I don't know enough about collapsing in non-Latin scripts to have an informed opinion. What does Opera 10.60 do?

>> For white-space-collapse: preserve-breaks;, I'm not totally confident what's
>> best, but I've been persuaded that Opera 10.60's behavior (CR is a break but
>> it coalesces with LF when appearing in a CRLF pair) is the thing I should
>> be wanting.
> 
> So you want CRLF normalization to happen at the CSS level in addition to the
> source markup level for text appearing in the DOM,

Yes.

> but not for text in generated content?

I didn't intend to express an opinion about generated content. I don't know how exactly code reuse works in implementation between DOM-appearing content and generated content, but I don't want to introduce any difficulties in that area.

-- 
Henri Sivonen
hsivonen@iki.fi
http://hsivonen.iki.fi/
Received on Tuesday, 3 August 2010 13:52:11 GMT

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