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[Bug 26304] New: Give reason/reference as to why BODY (and HTML) is always considered visible

From: <bugzilla@jessica.w3.org>
Date: Thu, 10 Jul 2014 11:22:19 +0000
To: public-browser-tools-testing@w3.org
Message-ID: <bug-26304-5015@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=26304

            Bug ID: 26304
           Summary: Give reason/reference as to why BODY (and HTML) is
                    always considered visible
           Product: Browser Test/Tools WG
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: WebDriver
          Assignee: public-browser-tools-testing@w3.org
          Reporter: ato@mozilla.com
        QA Contact: public-browser-tools-testing@w3.org
                CC: mike@w3.org

The visibility prose around the BODY element in the spec should be changed to
explain why it's always considered visible by WebDriver.  Also the bullet
points needs to be turned into an actual algorithm (covered by bug 26275).

Setting background-color or background-image on either the HTML or the first
BODY element triggers special casing.  If set they get transposed on to the
canvas painting area.

This means for example that if your BODY element has a background-color set and
you resize the viewport, the coloured area will always cover the whole
viewport.  The only two provisions are:

  * The element has display: none set
  * The element has visibility: hidden set

If the background-color is undefined in user style the default is
"transparent".  The CSS spec defines this to be undefined user agent behaviour,
but in all desktop and mobile browsers' base.css rules it means "white". 
However, this isn't true for HTML/CSS used in native OS widgets on such systems
as Firefox OS.  My suggestion is for WebDriver to only consider visibility
within the context of the current top-level browsing context and not
window-on-window transparency.

What this effectively means for WebDriver is that the canvas is always visible,
and because HTML (alternatively the first BODY) element's styling properties
are propagated on to it, it is consequently always visible.

This applies to both HTML and XHTML documents (even when served as
application/xhtml+xml).

The relevant CSS spec prose is here:

    http://dev.w3.org/csswg/css-backgrounds/#special-backgrounds

There's a bug in the current draft which has been logged here about display:
none and visibility: hidden (not in the spec at the time of writing this):

    http://lists.w3.org/Archives/Public/www-style/2014Jul/0137.html

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