W3C home > Mailing lists > Public > www-style@w3.org > January 2013

Re: [css3-positioning] "Top layer" for positioned elements?

From: Simon Fraser <smfr@me.com>
Date: Wed, 16 Jan 2013 20:33:35 -0800
Cc: www-style list <www-style@w3.org>
Message-id: <584BB6C7-5B1A-4DF1-A7A7-41E144B54190@me.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
On Jan 16, 2013, at 8:10 pm, "Tab Atkins Jr." <jackalmage@gmail.com> wrote:

> A decent number of recent specs outside of CSS (Fullscreen, <dialog>,
> others?) want the ability to put something "above everything else".
> (Of course, this doesn't really work, as multiple things can be "on
> top" at once, but all that's actually needed is "on top of everything,
> except possibly stuff that also wants to be on top").  Outside of
> specs, authors also want this kind of thing relatively often for their
> own purposes, often related (for example, doing author-build dialogs
> and similar things).
> In simple cases, this can be done with abspos, by setting z-index to a
> very high value.  However, this fails if the element is in a
> (pseudo-)stacking context.  As well, "very high value" isn't
> well-defined - many authors implicitly assume that implementations use
> a signed 32-bit int to store z-index (which happens to be true for
> several (all?) major implementations, but which shouldn't be depended
> on in general), and set z-index to 2 billion or so.  If impls ever
> change, or a new impl uses a smaller value (since this assumption
> isn't documented in any spec), the page will break.
> Instead, we could create a "top layer" for positioning stuff, which is
> separate from the "document layer".  This could be set with an
> additional value in z-index that can be specified alongside the number
> value.  Within the top-layer, z-index still works to position things
> relative to each other.  When positioned in the top layer, the element
> breaks out of any containing contexts, including pseudo-stackign
> contexts like 'opacity'.  (I'm unsure of whether this means they
> *won't* be affected by an ancestor's opacity/filter/etc, or if it'll
> be affected independently from the rest of the group they were
> originally in.  I suspect the former makes more sense and has better
> use-cases, and can perhaps be defined precisely in terms of "effects
> that create a pseudo-stacking context".)

I thought we were already spec'ing this as part of fullscreen/<dialog>?

Received on Thursday, 17 January 2013 04:34:04 UTC

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