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Re: [css-overflow][css-break] pathological fragment box generation

From: fantasai <fantasai.lists@inkedblade.net>
Date: Wed, 16 Sep 2015 18:49:16 -0400
To: "L. David Baron" <dbaron@dbaron.org>, Alan Stearns <stearns@adobe.com>
Cc: "www-style@w3.org" <www-style@w3.org>
Message-ID: <55F9F1EC.7070209@inkedblade.net>
On 04/06/2013 12:36 PM, L. David Baron wrote:
> On Thursday 2013-04-04 20:59 -0700, Alan Stearns wrote:
>> So the next step is to consider 0-height fragment boxes. Is there anything
>> needed for that case if you are choosing to slice?
>
> I'm inclined to think that css3-break should specify behavior such
> that there is *never* a situation where the next fragment starts in
> the same situation as the current fragment, even if the fragment is
> zero height.
>
> In other words, I would have a model where if the current position
> is at the top of a page/column/fragment (nothing placed yet), then
> something must be placed.
>
> If the (innermost) thing being placed is a a line (or portion
> thereof), a replaced block (or portion thereof), or margin, border,
> or padding, then placing at least one of these would be required.
> The height consumed for the blocks containing such object (whether
> fixed or auto height) would be determined by the height of the thing
> placed.
>
> On the other hand, if the thing that is placed is a portion of a
> fixed height that does not contain one of these things, such as the
> space below the lines in a fixed-height block that is taller than
> the space needed for its lines, then if that portion of height would
> be 0 (from the fragment height), then the line-height is used
> instead, and if that's 0 then the initial value of font-size is used
> instead.  I think my proposal is that these would be fallbacks
> rather than mimimums (that is, it would be possible to place less
> than these amounts if there were something at a specified but
> nonzero size).

We currently have the following text:
   https://drafts.csswg.org/css-break/#breaking-rules
   # To guarantee progress, fragmentainers are assumed to have a
   # minimum block size of 1px regardless of their used size.

The rest of the rules for unforced breaks are here:
   https://drafts.csswg.org/css-break/#unforced-breaks

There is nothing that explicitly guarantees placement at the top
of the page. It is suggested that the UA slice content if no full
fragment fits. However, it's not specified what happens if you
don't do that, though the spec seems to expect the content will]
overflow (rather than moving to a subsequent fragmentainer) if
not sliced.

I can take an action to clarify this point, if that seems acceptable.

~fantasai
Received on Wednesday, 16 September 2015 22:49:44 UTC

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