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Re: [css3-text] Behavior of text-decoration with differing font sizes, subscript, superscript, etc.

From: fantasai <fantasai.lists@inkedblade.net>
Date: Thu, 08 Nov 2012 18:18:34 -0800
Message-ID: <509C67FA.9020003@inkedblade.net>
To: www-style@w3.org
On 08/13/2012 05:08 AM, Aryeh Gregor wrote:
> Mozilla bug: https://bugzilla.mozilla.org/show_bug.cgi?id=778796
> Test-case 1: data:text/html,<!doctype html><s>foo<font size=7>bar</font>baz</s>
> The spec currently requires the line to be of consistent height and
> thickness in all three cases:
> """
> In determining the position and thickness of text decoration lines,
> user agents may consider the font sizes and dominant baselines of
> descendants, but for a given element's decoration must use the same
> position and thickness throughout each line box.
> """
> http://dev.w3.org/csswg/css3-text/#line-decoration
> I would like this reconsidered.  As fantasai points out on the linked
> bug, the requirement here usually makes sense with underline, because
> Western scripts are aligned along their baselines, which is where we
> put underlines.  But for line-through and overline, you can't put the
> line in a place that makes sense for both 12pt text and 36pt text.  If
> font sizes vary, you have to break up the line.  Also, even for
> underline, it makes sense to lower it for subscripts.
> I suggest one of the following two changes:
> * Mandate the behavior of IE and LibreOffice in my test-cases above.
> For a given element's decoration, an underline must remain at a
> consistent position and thickness throughout each continuous run of
> text in a single line box that has a consistent baseline.  (But if the
> baseline varies, the underline may be broken up.)  However,
> line-through and overline should be drawn at a height appropriate to
> the text and may differ in height or thickness within a line box.
> (Except maybe overlines should align for 'vertical-align: top',
> although it's a corner case.  Line-through is normally not drawn at
> the 50% mark, so we probably can't require line-throughs align for
> 'vertical-align: middle'.)
> * Remove the requirement entirely, so behavior is undefined.  I like
> undefined behavior a lot less, but we might have to do that if anyone
> thinks their behavior is better than IE's, or if it's too annoying to
> define (accounting for vertical-align, etc.).
> Basically, I think IE's behavior here should at least be legal, even
> if it's not mandated.  The Firefox/Opera behavior in the first
> test-case is clearly wrong, IMO, but it's what the spec currently
> requires.  IE's(/LibreOffice's) behavior makes the most sense to me.

Hi Aryeh,

The CSSWG discussed your issue. We didn't go with either suggestion,
because of additional considerations about maintaining a consistent
line position and thickness when, for example, the font face changes
without the font size changes.

The discussion starts in
and concludes in

The current spec text is available in the editor's draft at

Please let us know if this is satisfactory or if you have further
comments on this issue (including any suggested clarifications to
the new prose).


Received on Friday, 9 November 2012 02:19:04 UTC

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