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Re: CSS Device Adaptation and legacy meta tags and doctypes

From: Florian Rivoal <florianr@opera.com>
Date: Fri, 25 May 2012 15:31:54 +0200
To: "Kenneth Rohde Christiansen" <kenneth.christiansen@gmail.com>, "John Mellor" <johnme@chromium.org>
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>, "Rune Lillesveen" <rune@opera.com>
Message-ID: <op.weu87gwb4p7avi@localhost.localdomain>
I am not sure I want that text to be normative. By making the text  
normative, we'd push every browser into supporting these mechanisms, and  
make them more reliably usable by authors. In my mind, the goal of  
@viewport is to replace all these, not to legitimize them. The section  
explaining how to convert the meta viewport tag into @viewport is  
informative, and that's intentional.

On the other hand, once you have @viewport in place, supporting the
rest is fairly easy, and it might be worth doing for the sake of
interop.

Also, I am not sure a CSS spec is the right place to normatively define
parsing and associated error handling of html meta element directives.
Maybe the HTML spec, referencing this spec, could define these meta
elements. HTML would define the parsing and what set of @viewport
descriptors it corresponds to.

Maybe we could say that for documents unambiguously identified as
designed for small screen, the UA must have an UA stylesheet with every
@viewport descriptor set to auto, and leave it to the host language
to determine what it takes to unambiguously identify a document
as designed for small screen. HTML could (if they wanted) specify that
the HandheldFriendly meta element does that too.

All these reservations don't really apply to the XHTML-MP doctype, though,
so I think I'm fine with making that normative.

  - Florian


On Mon, 14 May 2012 16:25:31 +0200, John Mellor <johnme@chromium.org>  
wrote:

> I wrote a set of test pages to determine what browsers support these:
> jsbin.com/uyojoj/2
>
> And tested using the following browser versions:
> - (Legacy) Android Browser on Nexus S running ICS 4.0.4
> - Chrome for Android beta 2 on Nexus S running ICS 4.0.4
> - Firefox Aurora 14.0a2 (2012-05-13) on Nexus S running ICS 4.0.4
> - Internet Explorer Mobile 9 on Nokia Lumia 800 running WP7.5
> - Nokia Browser for N9 on Nokia N9 running MeeGo 1.2 Harmattan
> - Opera Mobile 12.00.ADR-1204201824 on Nexus S running ICS 4.0.4
> - Mobile Safari on iPod touch (4th gen) running iOS 5.1.1
>
> Here are the viewport widths that the browsers calculated on the 4 test
> pages:
>
> Test: \ Browser:|Android|Chrome |Firefox|  IE   | Nokia | Opera |Safari |
> ----------------+-------+-------+-------+-------+-------+-------+-------+
> Default         |  980  |  980  |  800? | 1024  |  980  |  980? |  980  |
> XHTML-MP        |  320  |  320  |  320  |  320  |  320  |  320  |  320  |
> HandheldFriendly|  320  |  320  |  800? |  320  |  320  |  980? |  980  |
> MobileOptimized |  320  |  320  |  800? |  320  |  320  |  980? |  980  |
>
> (there are question marks next to the Firefox and Opera widths since
> window.innerWidth did not match the observed viewport width, so I had to
> estimate these by eye)
>
> It seems that all browsers already treat the XHTML-MP doctype as  
> equivalent
> to a width=device-width viewport, so I agree with Kenneth that it would
> make sense for the Device Adaptation spec to explicitly formalize this
> defacto standard in a normative section.
>
> Handling of legacy HandheldFriendly and MobileOptimized viewport tags is
> less consistent, but adding these to the specification could also be
> useful, to improve interoperability.
>
> In both cases the order of precedence Kenneth suggested (whereby modern
> standards override legacy ones, irrespective of document order) seems  
> wise,
> as it reduces the risk of supporting the legacy methods.
>
> Cheers,
> John
>
> On Wed, May 9, 2012 at 11:49 AM, Kenneth Rohde Christiansen <
> kenneth.christiansen@gmail.com> wrote:
>
>> Hi there,
>>
>> 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)
>>
>> 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">
>>
>> Cheers,
>> Kenneth
>>
>> [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
>>
>> --
>> Kenneth Rohde Christiansen
>> Senior Engineer
>> Nokia Mobile Phones, Browser / WebKit team
>> Phone  +45 4093 0598 / E-mail kenneth at webkit.org
>>
>> http://codeposts.blogspot.com ﹆﹆﹆
Received on Friday, 25 May 2012 13:33:07 GMT

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