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[css3-regions] Section 7 (visual formatting) summary

From: Alan Stearns <stearns@adobe.com>
Date: Wed, 18 Apr 2012 12:54:09 -0700
To: "www-style@w3.org" <www-style@w3.org>
Message-ID: <CBB469F1.C3CC%stearns@adobe.com>
Hey all,

It was suggested that I try to summarize the details of section 7 [1] to
help people with first read-throughs.

The motivation for this section is to describe how fragments of named
flows are laid out in region chains, particularly when the size of a
region box may depend on the fragment it contains. The algorithm we
describe works towards the desired result while minimizing content reflow.

We introduce the notion of a "region flow content box" (RFCB) which is
sized according to the content fragment. Note that this fragment might be
determined by break points in the content AND/OR by constraints on the
region (as described in For instance, a region box with
height:100px will constrain the RFCB height and its content fragment in a
flow with no breaks defined.

There is a three-step process involved in laying out a region chain:

1. Resolve the heights of each fragment, using fragmentation rules and
region size constraints.

2. Lay out region boxes without named flow content, using the results from
step 1 if necessary.

3. Lay out named flow content in each RFCB, which now is sized depending
on the result from step 2.

It may be useful to read through the entire section including a close read
on the example in 7.4, then return to the earlier parts with that example
in mind.

We're very interested in feedback on this section - if there are any
mistakes in the algorithm or just places where we can be more clear,
please respond on the list.



[1] http://dev.w3.org/csswg/css3-regions/#regions-visual-formatting-details
Received on Wednesday, 18 April 2012 19:54:39 UTC

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