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Re: [css-regions] Handling circular dependencies between flows

From: Mihnea-Vlad Ovidenie <mihnea@adobe.com>
Date: Thu, 11 Oct 2012 13:08:34 +0100
To: Alan Stearns <stearns@adobe.com>, Mihai Balan <mibalan@adobe.com>, Andrei Bucur <abucur@adobe.com>, "www-style@w3.org" <www-style@w3.org>
Message-ID: <CC9C8D7E.2A6AA%mihnea@adobe.com>
Hi Alan,

On 10/11/12 12:36 AM, "Alan Stearns" <stearns@adobe.com> wrote:

>On 10/10/12 8:59 AM, "Alan Stearns" <stearns@adobe.com> wrote:
>>I would like to solve the basic circular reference problem by deciding
>>that these circular references do not create regions. So I'd change this
>>Likewise, if the block container is part
>>of the flow with name <ident>, then
>>the block container does not format
>>any content visually.
>>to this (and move it up in the definition to precede the text that
>>describes how regions are created)
>>If the block container is part
>>of the flow with name <ident>,
>>then the block container does
>>not become a CSS Region.
>This wording solves the case where a named flow contains a region for
>itself, but does not generally solve more complex circular dependencies
>that can arise. Following the advice on this morning's call, I am stealing
>some text from css4-images [1] and will replace the current sentence above
>with a section that reads:
>Named flows containing elements with the flow-from property set can
>produce nonsensical circular relationships, such as a named flow
>containing regions in its own region chain. These relationships can be
>easily and reliably detected and resolved, however, by keeping track of a
>dependency graph and using common cycle-detection algorithms.
>The dependency graph consists of edges such that:
>- Every named flow depends on its elements with the flow-from property set
>- Every element in a named flow with the flow-from property set to an
><ident> depends on the named flow with the <ident> name.
>If the graph contains a cycle, any elements with the flow-from property
>set to an <ident> participating in the cycle do not become CSS Regions.

Considering the following example:

    .flowA { flow-into: flowA; }
    .regionFlowA { flow-from: flowA; }
    .flowB { flow-into: flowB; }
    .regionFlowB { flow-from: flowB; }
<div id="div1" class="flowA">
    <div id="div2" class="regionFlowB"></div>
<div id="div3" class="flowB">
    <div id="div4" class="regionFlowA"></div>

Would create something like flowA -> div2 -> flowB -> div4 -> flowA and in
this case, both div2 and div4 (having flow-from) do not become regions.
Did I get it right?


>[1] http://dev.w3.org/csswg/css4-images/#element-cycles
Received on Thursday, 11 October 2012 12:09:10 UTC

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