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[CSS Box Alignment] Comments on CSS Box Alignment proposal

From: L. David Baron <dbaron@dbaron.org>
Date: Tue, 8 May 2012 11:11:31 +0200
To: www-style@w3.org
Message-ID: <20120508091131.GA19537@crum.dbaron.org>
A few comments on 
http://fantasai.inkedblade.net/style/specs/css3-align/ follow:

I don't think using 'true' as a property value works.  Even though
you don't mean it as a boolean, it looks like one.  Though it might
work if it were only allowed in combination with the other keywords.
(In fact, I'm not sure what it means for it to be used alone; it
seems like it's perhaps equivalent to 'true start' or 'true before',
though that's not clear.)

There also seems to be a bit of confusion (e.g., between the tables
in section 2, Overview of Alignment Properties) as to whether, for
the inline/main axis alignment, there is one property for default
alignment of children and alignment of contents, or whether there
are two separate ones:

 * For a start, the "sets default 'box-align' of children" should
   probably say "sets default 'box-justify'/'box-align' of
   children".

 * Additionally, though, the 'child-justify' property is mentioned in
   the table but not anywhere else.

However, this leads me to a set of closely related broader issues:

 * It seems to me that in the case where the parent lays out its
   children (and I mean children, not descendants) in one dimension,
   i.e., everything except grid, then:

   (a) there's no point distinguishing between 'content-align' and
   'child-align' since there's only one child at any given point in
   the secondary direction

   (b) the 'box-justify' property is meaningless since the children
   in the primary direction have to be aligned together (so I'm
   confused by the checkmark in the 'box-justify'/Block cell)
   *unless* there are external constraints on the space allocated to
   children (like constraints from other rows for the horizontal
   space given to cells within a table row) that don't (like they do
   for tables) actually change the size of the cells.

 * I'm confused about whichever of 'grid-row-align' and
   'grid-column-align' is in the block direction (I'm not sure this
   is fixed as the table suggests) is supposed to work when there is
   more than one grid item in a cell.  In particular, aren't the
   items going to be laid out as blocks in one dimension?  If so,
   how can they be *individually* aligned in that dimension?  (And
   isn't the ability to have multiple items in a cell the only
   reason that grid doesn't behave like tables (resizing the items)
   and avoid case (b) in the point above?)

These lead me to believe (if I've thought this through correctly,
which I'm not particularly confident of) that the six properties
given in the table should be collapsed into three:

 * 'box-justify' should be removed since you can't align an element
   in the direction in which its parent lays out children (despite
   that grid claims to have such a property without actually saying
   how it works -- unless I'm missing something here, which I
   certainly could be)

 * 'child-align' should be removed since there's no reason to
   separate it from 'content-align': if an element's children
   support 'box-align' or auto margins then 'content-align' is
   perfectly fine to use as the default rather than needing a
   separate property for this

 * 'child-justify' should likewise be removed since it sets the
   default for 'box-justify' on children, and I'm proposing removing
   'box-justify', and for the same reasons as 'child-align'

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                           http://www.mozilla.org/   𝄂
Received on Tuesday, 8 May 2012 09:12:20 GMT

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