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Re: CSS Device Adaptation and legacy meta tags and doctypes

From: Kenneth Rohde Christiansen <kenneth.christiansen@gmail.com>
Date: Wed, 28 Aug 2013 17:12:57 +0200
Message-ID: <CAEC208tMvhOC+q49prrYXWDcf0=iWrTS67TboPFvHq=gwPCoYA@mail.gmail.com>
To: Rune Lillesveen <rune@opera.com>
Cc: www-style list <www-style@w3.org>, Peter Beverloo <peter@chromium.org>, Hugo Parente Lima <hugo.lima@openbossa.org>, Ojan Vafai <ojan@chromium.org>, John Mellor <johnme@chromium.org>, "Kostiainen, Anssi" <anssi.kostiainen@intel.com>
Hi there Rune,

On Mon, Aug 26, 2013 at 1:49 PM, Rune Lillesveen <rune@opera.com> wrote:
> On Wed, May 9, 2012 at 12:49 PM, Kenneth Rohde Christiansen
> <kenneth.christiansen@gmail.com> wrote:
>> Hi there,
> Hi, resurrecting this thread.


>> Following a discussion on webkit-dev [1], we would like to have added
>> a nomative section in the CSS Device Adaptation spec [2], specifying
>> how to handle legacy viewport tags, such as HandheldFriendly.
>> The spec already briefly talks about XHTML-MP in the following:
>> "Certain DOCTYPEs (for instance XHTML Mobile Profile) are used to recognize
>> mobile documents which are assumed to be designed for handheld devices, hence
>> using the viewport size as the initial containing block size."
>> The Nokia N9 browser, WP7 Internet Explorer and Android already
>> implement such support. And testing shows that iOS at least does
>> similar things for XHTML-MP.
>> The IE team even has a blog post explaining how it works [3]
>> Basically there is a priority:
>> XHTML-MP doctype (overrides default configuration)
>> HandheldFriendly meta tag (overrides XHTML-MP doctype)
>> MobileOptimized (overrides HandheldFriendly, etc)
>> viewport (overrides MobileOptimized etc)
> I've tried to twist my brain around this and I think a prioritization
> makes sense. Currently, the spec says that meta viewport elements are
> cascaded together with @viewport rules. It probably makes more sense
> with a prioritization where meta viewport rules, and other legacy
> tags, are dropped in the presence of @viewport rules in a UA
> supporting @viewport. Otherwise there will be an unpredictable mix of
> descriptors from the various legacy tags and the @viewport descriptors
> depending on which of the legacy tags are supported in a given UA.

I have the same feeling. If the web site has @viewport and a viewport
meta, the latter is probably there to handle browsers not supporting
@viewport and site author doesn't intent the two to interact, which
might force the author to resort to browser sniffing instead :-(

> I think the XHTML-MP doctype should be an expection, though.

I agree that it is an exception.

> doctype should affect the _UA_ styles. XHTML-MP documents is not a
> legacy tag in the same sense, and a UA that implements only @viewport
> would still have separate UA styles which don't have the @viewport {
> min-width: 980px } as the HTML/HTML5 documents would have.
> The legacy tags should be on the author level of the cascade, though.
> So, the cascade would be something like this:
> 1. UA stylesheets (different @viewport for HTML and XHTML-MP)
> 2. User stylesheets

Should the user be able to overwrite differently for HTML and XHTML-MP?

> 3. Author style - only one of the sources below picked for the
> cascading. Based on presence - listed in increasing priority.
> 3.1. HandheldFriendly
> 3.2. MobileOptimized
> 3.3. Meta Viewport  (The 980px default width behavior should be on the
> author level here before adding meta tags instead of having it at UA
> level as mentioned in Section 11 of css-device-adapt)
> 3.4. @viewport
> I do agree that the legacy handling doesn't belong in the
> css-device-adapt spec. It's there for historical reasons and the fact
> that it's easier to keep it up-to-date with changes in @viewport
> descriptors while the spec evolves. I'm fine with moving legacy tag
> handling into HTML as normative.

Fine with me too, but maybe later when the spec is more stable? and
this has implementations?


>> The XHTML-MP doctype would correspond to the following viewport meta
>> tag: <meta name="viewport" content="width=device-width,
>> height=device-height, initial-scale=1">
>> The same counts for HandheldFriendly (and MobileOptimized, in the case
>> the content attribute is missing or not parseable)
>> Else <meta name="MobileOptimized" content="320"> would to correspond
>> to  <meta name="viewport" content="width=320, initial-scale=1">
>> [1] http://thread.gmane.org/gmane.os.opendarwin.webkit.devel/20536
>> [2] http://www.w3.org/TR/css-device-adapt/
>> [3] http://blogs.msdn.com/b/iemobile/archive/2010/11/22/the-ie-mobile-viewport-on-windows-phone-7.aspx
> --
> Rune Lillesveen

Kenneth Rohde Christiansen
Senior Engineer, WebKit, Qt, EFL
Phone  +45 4294 9458 / E-mail kenneth at webkit.org

Received on Wednesday, 28 August 2013 15:13:24 UTC

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