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Re: [CSS21] Issues with inline formatting model (particularly 10.8)

From: Anton Prowse <prowse@moonhenge.net>
Date: Tue, 01 Sep 2009 23:37:41 +0200
Message-ID: <4A9D9425.5080207@moonhenge.net>
To: "www-style@w3.org" <www-style@w3.org>
Anton Prowse wrote:
> 10.8.1, 'vertical-align' property
> (http://www.w3.org/TR/CSS21/visudet.html#propdef-vertical-align) :
> 
>   # This property affects the vertical positioning inside a line box of
>   # the boxes generated by an inline-level element.
>   #
>   # The following values only have meaning with respect to a parent
>   # inline-level element, or to the strut of a parent block-level,
>   # table-cell, table-caption or inline-block element.
>   #
>   # baseline
>   #     Align the baseline of the box with the baseline of the parent
>   #     box.  If the box doesn't have a baseline, align the bottom
>   #     margin edge with the parent's baseline.
> 
> 
> Issue 10a:  If 'strut' is going to be used normatively, it should be
> defined explicitly in 10.8.1 rather than by example ('what TeX calls a
> "strut"').
> 
> 
> Issue 10b:  [...]
> 

Some more issues come to light from the recent correspondence about
baselines and struts.


10.8.1, 'vertical-align' property :

   # The following values only have meaning with respect to a parent
   # inline-level element, or to the strut of a parent block-level,
   # table-cell, table-caption or inline-block element.


Issue 10c:  The wording suggests that a strut is a property of a several
different types of element.  This is incorrect; a strut is a property of
a line box.  This is essentially the same issue as Issue 8 as discussed
in [1].

   # baseline
   #     Align the baseline of the box with the baseline of the parent
   #     box. If the box doesn't have a baseline, align the bottom margin
   #     edge with the parent's baseline.
   # middle
   #     Align the vertical midpoint of the box with the baseline of the
   #     parent box plus half the x-height of the parent.

Then,

s/parent box/parent box or strut/
s/parent's/parent's or strut's/

since redefining "parent (box)" to possibly mean "strut" is pretty ugly.


Issue 10d:  What is the baseline of an empty inline box?  Section 9.4.2
(Inline formatting context) states that text inside inline boxes has a
baseline, which is presumed to determine the baseline of the inline box
itself (see David Baron's and my discussion of Issue 10b in [2]).  If
such an inline box is empty, a strut is presumed to be used, although
the spec only discusses struts in relation to line boxes
(notwithstanding Issue 10c).


Issue 10e:  In the description of the 'baseline' value, which
inline-level/table-cell boxes don't have a baseline?  Boxes of type
inline-block, inline-table and table-cell are explicitly defined to have
one.  Boxes of type run-in which become inline boxes are assumed to
behave like normal inline boxes.  But how do such boxes behave?  Boxes
resulting from non-replaced inlines are presumed to have a baseline, as
described in Issue 10d.   On the other hand it seems natural to treat
the inline boxes resulting from inline replaced elements to have no
baseline, but this is not stated anywhere; perhaps it can /very/ vaguely
be concluded by comparing 10.6.1 with 10.6.2 (calculating height and
margins for inline non-replaced elements and inline replaced elements
respectively).


[1] http://lists.w3.org/Archives/Public/www-style/2009Aug/0655.html
[2] http://lists.w3.org/Archives/Public/www-style/2009May/0191.html

Cheers,
Anton Prowse
http://dev.moonhenge.net
Received on Tuesday, 1 September 2009 21:39:41 GMT

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