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Re: Text-selecting/highlighting content area or line box? (was [CSS 2.1] [Section 9.5.1] Vertical positioning of floating boxes)

From: Gérard Talbot <www-style@gtalbot.org>
Date: Thu, 15 Dec 2011 11:17:11 -0800
Message-ID: <778b54cfc5776d93358f4855ff20b715.squirrel@gtalbot.org>
To: "Alan Gresley" <alan@css-class.com>
Cc: "W3C www-style mailing list" <www-style@w3.org>

Le Mer 14 décembre 2011 23:57, Alan Gresley a écrit :
> On 8/12/2011 9:59 AM, "Gérard Talbot" wrote:
>>
>> Le Dim 12 septembre 2010 23:01, Alan Gresley a écrit :
>>> Gérard Talbot wrote:
>>
>> GT>>  3- When text-selecting/highlighting a chunk of text (by dragging
>> the
>>>> mouse), we are in fact hightlighting what exactly? I think we are
>>>> highlighting the content area; I think we are not highlighting the
>>>> line
>>>> box. Am I wrong?
>>>
>>>
>> AG>  You are highlighting line boxes. Sort of like when you hover line
>>> boxes and the mouse pointer changes from a cursor to a text (indicates
>>> text that may be selected. Often rendered as an I-beam.).
>>
>>
>> Alan,
>>
>> In this testpage
>>
>> http://test.csswg.org/suites/css2.1/20110323/html4/c527-font-001.htm
>>
>> when I text-select/highlight a chunk of text (by dragging the mouse), I
>> think we are highlighting (in reverse video) the content area if we are
>> using Firefox 8.0 or Opera 11.60 or Konqueror 4.7.3 (I will check other
>> browsers later).  The vertical white gap between highlighted content
>> area
>> is the leading (or top-half-leading of current line box plus
>> bottom-half-leading of previous line box) which is 9px in that page.
>
> That is what I observe in Firefox 8.0 or Opera 11.60 and IE9 (Windows).
>
>> If we are using Chrome 15.0.874.121, then we are highlighting the
>> content
>> area plus the top-half-leading of the line box plus the
>> bottom-half-leading of the previous line box. I reached such conclusion
>> after creating this testcase:
>>
>> http://www.gtalbot.org/BrowserBugsSection/css21testsuite/line-height-bleed-003-GT.html
>>
>> which is supposed to improve the
>>
>> [RC6]
>> http://test.csswg.org/suites/css2.1/20110323/html4/line-height-bleed-003.htm
>>
>> [nightly-unstable]
>> http://test.csswg.org/suites/css2.1/nightly-unstable/html4/line-height-bleed-003.htm
>>
>> regards, Gérard
>
>
> Hello Gérard,
>
> What Safari 5.1.2 and Chrome 16 (on Windows 7) does when highlighting
> seems to be very wrong.
>
> I understand the like box as something that is the height of the glyphs
> or ideographs that are contained within such a line box and depending on
> the line-height (from baseline to baseline of successive line boxes),
> the line boxes can be either be spaced well apart or overlapping. From
> Wikipedia [1] is this:
>
>    | In typography, leading (play /ˈlɛdɪŋ/) refers to
>    | the distance between the baselines of successive
>    | lines of type.
>
> When you drag the cursor to highlight a line in WebKit, what is being
> highlighted is a 'pseudo line-height box' (a random name) that begins at
> the bottom of box that contains the glyphs or ideographs. In your text
> case 'line-height-bleed-003-GT.html' this seems to be affected by lines
> of different heights.
>
> Try highlighting the Ahem text in this test.


http://www.gtalbot.org/BrowserBugsSection/css21testsuite/Highlighting-line-box-tests-001.html

>
> <!DOCTYPE html>
>
> <style type="text/css">
>      div {font: 100px/0.5 Ahem;}
> </style>
>
>   <div><br>X pÉ</div>
>
> Only the bottom half of the box is highlighted and this equals the
> height of the line-height. When you have a mixed of different glyph or
> ideographs base (not Latin), this becomes more haphazard.

Huh... when you have a mixed of different glyphs, then

"The line box height is the distance between the uppermost box top and the
lowermost box bottom."
http://www.w3.org/TR/CSS21/visudet.html#line-height

should still be true.




> Please try highlighting the various lines of text here (compare WebKit
> and then say Firefox).
>
> http://css-class.com/test/css/text/line-height-descenders-mixed-script.htm
>

I can see what you mean by "pseudo line-height box".


> What I also note in WebKit (Windows). If you have several lines of text,
> when you reach a line box on a new line, the full length of the
> block-level element is also highlighted that is proceeding the new line.
>
> CSS2.1 is (or was) somewhat unclear about line boxes and how line-height
> was used. Please see this list messages [2] where I have mentioned this
> and also this list message [3] that give the reasoning and history
> behind current implementation behaviour.

I will read this.

regards, Gérard

>
> 1. http://en.wikipedia.org/wiki/Leading
> 2. http://lists.w3.org/Archives/Public/www-style/2011Jan/0116.html
> 3. http://lists.w3.org/Archives/Public/www-style/2010Dec/0448.html
>
>
> --
> Alan Gresley
> http://css-3d.org/
> http://css-class.com/
>
>


-- 
CSS 2.1 Test suite RC6, March 23rd 2011
http://test.csswg.org/suites/css2.1/20110323/html4/toc.html

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Received on Thursday, 15 December 2011 19:17:53 GMT

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