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Re: [css3-flexbox] overflow property

From: Anton Prowse <prowse@moonhenge.net>
Date: Mon, 14 May 2012 13:31:26 +0200
Message-ID: <4FB0ED0E.5000702@moonhenge.net>
To: www-style@w3.org
CC: fantasai <fantasai.lists@inkedblade.net>
On 13/05/2012 12:42, fantasai wrote:
> On 05/11/2012 06:18 AM, Tab Atkins Jr. wrote:
>> On Fri, May 11, 2012 at 2:58 PM, Morten Stenshorne<mstensho@opera.com>
>> wrote:
>>> Should the 'overflow' property apply to flexboxes? Implementations do
>>> support it, and I think it makes sense to do so.
>>>
>>> However, the flexbox spec (20120510) says that "Flexboxes are not block
>>> containers", and CSS21 says that 'overflow' applies to block containers
>>> only.
>>>
>>> BTW: When it comes to "the other non-block container thing", namely
>>> tables, it looks like we have all agreed to honor overflow:hidden, while
>>> overflow:scroll and overflow:auto are treated as overflow:visible...
>>
>> CSS21 needs fixing there. Anton, fantasai, you led me astray! Y'all
>> told me that it doesn't make sense to call it a block context!
>
> Because it isn't! You aren't formatting flexbox items as block flow.
>
> We could say "block containers and boxes that estabish a formatting
> context", but I'm not sure how that interacts with tables. The table
> box presumably establishes a table formatting context.

Actually it works fine for tables, since the Applies To line for 
'overflow' should have been "block containers and table boxes" anyway 
(see https://www.w3.org/Bugs/Public/show_bug.cgi?id=15381 ).

I support your proposed wording, but I think it ought to be accompanied 
by a modification to 9.4 in which the term "formatting context" is 
introduced, and to Chapter 17, as follows.

In 9.4 (Normal flow), replace:

   # Boxes in the normal flow belong to a formatting context, which may
   # be block or inline, but not both simultaneously. Block-level boxes
   # participate in a block formatting context. Inline-level boxes
   # participate in an inline formatting context.

with:

   | Boxes in the normal flow belong to a formatting context, which in
   | CSS21 may be block, inline or table. In future levels of CSS, other
   | types of formatting context will be introduced. Block-level boxes
   | participate in a block formatting context. Inline-level boxes
   | participate in an inline formatting context. Table formatting
   | contexts are described in the chapter on _tables_.

[Note that I omitted the bit about "not both simultaneously" because 
it's not actually true:

<div style="overflow:hidden">text</div>

The div establishes a BFC and an inline formatting context (IFC), unless 
we're claiming that there's an anonymous block box wrapping the text. 
(Although, as it happens, I would prefer it if a block container box 
were never allowed to establish an inline formatting context; I /would/ 
insist on there being anonymous block-level IFC boxes that wrap all 
inline-level content.  That would make block container boxes truer to 
their name, and solve various other little mysteries in the box tree, 
albeit at the cost of introducing a ton of new boxes. I'd welcome 
comments from implementers; I think those new boxes would be purely an 
editorial device without needing to exist physically.]

In 17.4 (Tables in the visual formatting model), replace:

   # [...] The table wrapper box establishes a block formatting context.
   # [...]

with:

   # [...] The table wrapper box establishes a block formatting context,
   # and the table box establishes a table formatting context. [...]

In 17.5 (Visual layout of table contents), replace:

   # Internal table elements generate rectangular boxes with content and
   # borders. Cells have padding as well. Internal table elements do not
   # have margins.

with:

   # Internal table elements generate rectangular boxes which
   # participate in the table formatting context established by the
   # table box. These boxes have content and borders, and cells have
   # padding as well. Internal table elements do not have margins.


Cheers,
Anton Prowse
http://dev.moonhenge.net
Received on Monday, 14 May 2012 11:32:07 GMT

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