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Re: [css3-values][css3-page] Viewport-percentage length units in the page context.

From: Anton Prowse <prowse@moonhenge.net>
Date: Sat, 20 Oct 2012 18:18:40 +0200
Message-ID: <5082CEE0.70501@moonhenge.net>
To: WWW Style <www-style@w3.org>
CC: "Tab Atkins Jr." <jackalmage@gmail.com>, Simon Sapin <simon.sapin@kozea.fr>, Leif Arne Storset <lstorset@opera.com>
On 19/10/2012 21:46, Tab Atkins Jr. wrote:
>
> No, this doesn't work.  It *will* change the layout, because the page
> size *is* the initial containing block for the contents on that page.

On 19/10/2012 22:36, Tab Atkins Jr. wrote:
> On Fri, Oct 19, 2012 at 1:26 PM, Simon Sapin <simon.sapin@kozea.fr> wrote:
>>
>> Second issue: if an element is fragmented over multiple pages, the page size
>> may vary. However the computed value for eg. 'margin-left: 3vw' is supposed
>> to be absolute. Does that mean that the element has *multiple* sets of
>> computed values, one for each page?
>
> Ah, good point.  They definitely have multiple sets of layout values -
> one per fragment.  Computed values are meant to be attached to
> elements, though.  This is a more interesting question.  Dunno!

5.1.2 of css3-values ED says:

   # The viewport-percentage lengths are relative to the size of
   # the initial containing block.

and Section 4 of css3-page ED says:

   # The edges of the page area on the first page establish the
   # rectangle that is the initial containing block of the document.

There's only one ICB in paged media (indeed in any media), and it's 
established by the first page.  Hence vw etc are relative to that, and 
don't vary depending on which page you're currently working with.

Given that I seem to be having the same wheelspin in [1], in the context 
of absolute positioning in paged media, I'm wondering I'm 
misunderstanding something fundamental about how ICB works in paged media...

[1] http://lists.w3.org/Archives/Public/www-style/2012Oct/0565.html

Cheers,
Anton Prowse
http://dev.moonhenge.net
Received on Saturday, 20 October 2012 16:19:11 GMT

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