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[Bug 19277] Relationship and precedence of hidden="" and display:none should be clarified/defined

From: <bugzilla@jessica.w3.org>
Date: Mon, 26 Nov 2012 16:21:20 +0000
To: public-html-bugzilla@w3.org
Message-ID: <bug-19277-2486-4GGRJMF54o@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=19277

--- Comment #16 from Boris Zbarsky <bzbarsky@mit.edu> ---
Sorry for the lag here: I wasn't getting bugmail for a while there, so was
unaware of this conversation.

Trying to answer the questions asked of me in some order:

1)  Making things with @hidden "display: none ! important" in the UA stylesheet
would mean web pags cannot override the display at all, ever.  Which is
suboptimal, possibly.  It would also, at least in the case of Gecko, require
either accepting a small performance hit on every pageload because the selector
"[hidden]" would be matched against every single element or building entirely
new styling machinery for this one attribute, neither one of which fills me
with glee.  But we could manage that, perhaps.

2)  I believe, though I could be wrong, that the accessibility model exposed by
Gecko is based on the CSS box model.  No CSS box (e.g. display:none) means no
accessible object.  Hence the observed display:none behavior.  I have no idea
to what extent this is true for other browsers nor how difficult it is to
change in Gecko.

3)  In general, adding one-off exceptions to CSS processing carries a very
heavy implementation burden due to the complexity it causes.  Absent extremely
strong justification, I would be opposed to adding such exceptions.

4)  <div hidden> and <div hidden=""> and <div hidden="hidden"> all behave
identically.

5)  I would very very strongly prefer that whatever we decide to do here is
done via defining styles on elements with the "hidden" attribute set instead of
defining new magic.  See item 3.  What those styles should be obviously depends
on the exact desired semantics of @hidden...

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