filter should be defined to establish a containing block for fixed and absolutely positioned elements

[dbaron]

As resolved in http://www.w3.org/2015/02/10-fx-minutes.html#action02 and mentioned in the introduction to the spec, 'filter' not 'none' should create a containing block for absolutely and fixed positioned elements.

(Per https://lists.w3.org/Archives/Public/public-fx/2015OctDec/0035.html I think we should explicitly state that it also applies to absolutely positioned elements, and not just assume the reader can infer that absolute implies fixed as well, since nothing says that.)

[dholbert]

CC @erikdahlstrom @dirkschulze can we get this addressed?

[chrishtr]

I'm concerned that this will make it impossible to apply a filter (e.g., for accessibility to change the color) to an entire webpage without messing up fixed-position elements. This is because there is no HTML
element exposed to the developer which is the containing block for fixed-position elements.

[mstange]

That is true and a bit unfortunate.

In browsers that support backdrop-filter, you can put a fixed element on top of everything (with pointer-events: none) and apply the filter you want as that element's backdrop filter. But that's more a workaround than a true solution.

A better solution would be the ability to set the filter directly on the containing block for fixe-position elements. I don't know how you would expose that.

[richschwer]

I may have misunderstood your comment, but, aria-hidden only hides the container and its descendants from an AT (screen reader/screen magnifier, etc.) and it does not impact the visibility of the element or its descendants.
 
Rich Schwerdtfeger
 
 
----- Original message -----From: chrishtr notifications@github.comTo: w3c/fxtf-drafts fxtf-drafts@noreply.github.comCc:Subject: Re: [w3c/fxtf-drafts] filter should be defined to establish a containing block for fixed and absolutely positioned elements (#11)Date: Wed, Nov 2, 2016 1:04 PM 
I'm concerned that this will make it impossible to apply a filter (e.g., for accessibility to change the color) to an entire webpage without messing up fixed-position elements. This is because there is no HTMLelement exposed to the developer which is the containing block for fixed-position elements.
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[chrishtr]

My comment was not about aria. It was about losing the ability to provide a color or other filter extension
for web pages, without causing the page to display fixed-position elements incorrectly.

[mstange]

The only other idea I have for addressing that case is: We could make filter on the root element special, similar to what we do for overflow and background, and make it always propagate up to the containing block for position:fixed elements.

[bzbarsky]

@dirkschulze @erikdahlstrom any chance of this spec getting updated per the resolution mentioned above?

[chrishtr]

If there is consensus, I'd like to try to make this change in Chrome.

[bzbarsky]

Note that Firefox has been shipping this behavior for a while now, as I understand, since that was what the working group resolved...