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[css3-regions] Auto-generation (issue 15186)

From: Alan Stearns <stearns@adobe.com>
Date: Thu, 11 Oct 2012 12:43:30 -0700
To: "www-style@w3.org" <www-style@w3.org>
Message-ID: <CC9C6F72.17A9A%stearns@adobe.com>
Issue 15186 [1] in CSS Regions contains this concern:

---
If the content poured into the regions take up more space than the
fixed set of regions can hold, no additional regions will be generated
automatically.
---

I agree that auto-generation of boxes is very useful in many
circumstances, and I support auto-generation in the multicol,
page-templates and overflow proposals. But I am going to argue that the
CSS Regions module does not require auto-generation, for the same reason
that regular elements do not *require* auto-generation of additional boxes
to contain their overflow.

When you style a div and its contents in CSS, overflow can happen. There
are methods for dealing with  overflow. One is to specify height as auto,
to allow the container to size to its contents. If the height of the
container must be constrained, you can turn on a scrollbar or (in the
future) use the proposed overflow:fragments mechanism.

Exactly the same methods are available to region chains. For the simplest
case of a region chain consisting of a single CSS Region, the situation is
exactly the same as the div above. You can specify the region's height as
auto, give it a scrollbar, or use any other available method for dealing
with overflow. The region can respond to the named flow contents in just
the same way a normal div responds to its own contents. In considering
more complicated region chains, it can be useful to begin at the end of
the region chain and work backwards. If you add one or more regions to the
beginning of the simplest region chain, nothing has changed. The last
region in the chain still has all of the normal overflow solutions
available for the fragment it contains.

So contrary to the concerns in the issue, the draft as it stands can
handle unexpected changes in content, font usage or user styles in a fixed
set of regions - in exactly the same way that normal elements handle such
differences. And by hooking in to the basic workings of CSS in this way,
region chains can take advantage of new mechanisms such as
overflow:fragments that are invented. So regions will be compatible with
future auto-generation mechanisms (such as what's proposed in page
templates), but it's not required to define an auto-generation mechanism
in the CSS Regions module itself. The concerns in this issue can be
addressed by using the methods for dealing with overflow that already
exist.

Thanks,

Alan

[1] https://www.w3.org/Bugs/Public/show_bug.cgi?id=15186
Received on Thursday, 11 October 2012 19:44:00 GMT

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