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Re: [css3-regions] writing mode and directionality for flows

From: David Hyatt <hyatt@apple.com>
Date: Mon, 15 Aug 2011 15:02:02 -0500
Cc: Vincent Hardy <vhardy@adobe.com>, "www-style@w3.org CSS" <www-style@w3.org>
Message-id: <38D80C48-5E98-4758-B176-05F5462D597D@apple.com>
To: Alex Mogilevsky <alexmog@microsoft.com>
On Aug 14, 2011, at 2:09 PM, Alex Mogilevsky wrote:

> Considering that in paged media first page is the ICB, first region will be ICB too (right?), then it would be reasonable to expect that root writing mode is that of the first region element.
> 

I assume it would be something like that. I do wonder how fixed positioned elements placed into a flow are supposed to work though. Do they get sliced up into the regions, or should we just say that -webkit-flow does not apply to fixed positioned elements? I'm inclined to just say that -webkit-flow doesn't apply to fixed positioning.

I think we may need to formalize the notion of a containing block that represents the flow itself before it's sliced up into all the regions. Then the portion of that strip that is placed into the first region would be the "ICB" for absolute positioned descendants, etc.

Once you have a formal notion of this single "flow thread" that goes through all the regions and that is itself a block, then I think some definitions become simpler/more obvious. For example you can see clearly that you desire one default pagination direction, i.e., one single way of making the slices in the strip, either top to bottom in horizontal-tb, right to left in vertical-rl, or left to right in vertical-lr.

I also think if we're willing to give up certain features, e.g., variable width paginated blocks, we could come up with simpler ways to handle variable width regions, such as just supporting it on lines rather than on blocks…. for example by imagining that narrower regions have synthetic floats introduced along their edges that lines would avoid. This would allow you to still have the notion of a single flow thread that has the same width across all regions, and lines would fit within narrower regions because of these synthetic floats we put in.  Lots of stuff would still work (lines would look good, text-align would work, etc.), but then some things would not, e.g., expecting a block with a border to actually have different widths if paginated across a region.

dave
Received on Monday, 15 August 2011 20:03:02 GMT

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