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[css4-image] element() comments

From: Robert O'Callahan <robert@ocallahan.org>
Date: Mon, 3 Feb 2014 11:06:05 +1300
Message-ID: <CAOp6jLai3Q2UnFCs4FMDEUJyo_OtFXkSV0iAxR0OuS8+xMd-zg@mail.gmail.com>
To: www-style <www-style@w3.org>, "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: Nicholas Cameron <ncameron@mozilla.com>
http://dev.w3.org/csswg/css-images/#element-notation

> The function represents an image with its intrinsic size equal to the decorated
> bounding box of the referenced element
>

Giving element() an intrinsic size is actually super bad. It creates almost
arbitrarily bad circular layout dependencies; e.g. any <li> element's size
can now depend on the size of any other element in the document! Detecting
and fixing the circularity isn't easy either, because you can combine this
with existing dependencies to create cycles in all kinds of ways. Since
this is mostly useless anyway, I propose specifying that element()s have no
intrinsic dimensions at all.

Regarding issue #9, I think the best solution is to amend the condition "an
element that is rendered and is not a descendant of a replaced element" to
also require that the element have a stacking context. We could specify
that directly, but it might be simpler for authors to just require it have
non-auto z-index and non-static position.

Rob
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Received on Sunday, 2 February 2014 22:06:33 UTC

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