This was was cloned from bug 15133 as part of operation convergence.
Originally filed: 2011-12-09 23:19:00 +0000

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 #0   contributor@whatwg.org                          2011-12-09 23:19:46 +0000 
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Specification: http://www.whatwg.org/specs/web-apps/current-work/multipage/editing.html
Multipage: http://www.whatwg.org/C#the-hidden-attribute
Complete: http://www.whatwg.org/c#the-hidden-attribute

Comment:
Please explain how hidden=true interacts with plugin loading.  Should it be
treated as display:none?

Posted from: 173.164.128.209
User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_2) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.0 Safari/535.11
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 #1   Eric Seidel                                     2011-12-09 23:23:15 +0000 
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See https://bugs.webkit.org/show_bug.cgi?id=56575 for context on how WebKit currently has trouble with hidden=true plugins, since we need to not load display:none plugins:
http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2011-November/033732.html
but at least that author expects hidden=true to not act like display: none.
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 #2   Ian 'Hixie' Hickson                             2012-01-31 22:55:54 +0000 
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Well first, hidden=true is bogus. hidden="" is a boolean attribute, meaning it's either present or absent, and its value, if any, has to be the same as its name.

But that's irrelevant here since this is a legacy page, not a page using the new hidden="" attribute.

If we have to address this, I propose doing it by changing the [hidden] rule in ua.css to:

   [hidden]:not(object):not(embed), ... { }

   object[hidden], embed[hidden] { width: 0; height: 0; }
   object[hidden] { overflow: hidden; }

...in the ua.css file.
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