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Re: [css-device-adapt] Accepting semi-colons as a separator for meta-viewport

From: Peter Beverloo <beverloo@google.com>
Date: Fri, 21 Oct 2011 11:35:41 +0100
Message-ID: <CALt3x6kBCzJvtaDirredHa9_nf5gW-55f46h8fOgBeqo4ectsA@mail.gmail.com>
To: Rune Lillesveen <rune@opera.com>
Cc: www-style@w3.org
On Fri, Oct 21, 2011 at 10:14 AM, Rune Lillesveen <rune@opera.com> wrote:
> On Thu, 20 Oct 2011 19:12:01 +0200, Peter Beverloo <beverloo@google.com>
> wrote:
>
>> The CSS Device Adapt specification defines a parsing algorithm[1] for
>> the meta-element viewport content, which has been based on WebKit's
>> implementation that shipped with iOS4. This algorithm only accepts
>> commas as separators between properties.
>
> First, it's in a non-normative section, and we want UAs to move towards an
> @viewport implementation. That being said, it's there to suggest a mapping
> between viewport meta and @viewport in a transition phase.
>
>> In reality, web authors are using both commas as semi-colons. A wide
>> range of websites, including CNN[2], Flickr[3] and Reddit[4] depend on
>> this behavior, which has led at least Mozilla and Microsoft to
>> implement it and, in case of the latter, write about it[5].
>
> Yes, and they have to add some combination of scale properties to compensate
> for the fact that "width=device-width;" is the same as "width=0" in Safari
> and Opera (see comments for the mentioned sites below).

The fact that the numeric properties' values are being recognized are
purely a work-around, which, in case of WebKit-based browsers, depends
on disregarding trailing garbage for numeric values to parse these
correctly (warnings for which are being shown in Web Inspector).

>> I think the specification should adapt to reflect what authors are
>> doing. While it's unfortunate that the divergence between commas and
>> semi-colons happened, it's important for compatibility among mobile
>> browsers.
>
> Two alternative proposed changes:
>
> 1. Keep the algorithm as it is and mention that some implementations accept
> ';' as a separator in addition to ','.
>
> 2. Modify the algorithm to include ';' as a separator and say that it's
> based on the Safari implementation with the ';' added as a recognized
> separator.

Your second alternative proposal describes the change I'm proposing,
with the addition of a note saying that it differs there from Safari's
implementation.

>> [1] http://dev.w3.org/csswg/css-device-adapt/#parsing-algorithm
>> [2] http://m.cnn.com
>
> Does not give me a viewport meta in Opera.

I verified that they do give a viewport meta in WebKit, so they
probably are sniffing for the browser. For reference:

<meta xmlns="http://www.w3.org/1999/xhtml"
      name="viewport"
      content="initial-scale=1.0; maximum-scale=1.0; user-scalable=0;" />

>> [3] http://m.flickr.com
>
> "width=device-width; initial-scale=1.0; maximum-scale=1.0; user-scalable=0;"
>
> Works in Safari because the over-constraining scale values cause the width
> to end up at device-width anyway. This would not have worked in Safari or
> Opera: "width=device-width; user-scalable=0;".

As said, this is because strtod() accepts trailing garbage, which
applies to the numeric values. I don't expect authors to know about
this difference.

Peter

>> [4] http://www.reddit.com/.compact (or http://m.reddit.com/)
>
> Same as for m.flickr.com.
>
>> [5]
>> http://blogs.msdn.com/b/iemobile/archive/2010/11/22/the-ie-mobile-viewport-on-windows-phone-7.aspx
>
> --
> Rune Lillesveen
> Layout Group Manager
> Core Technology Department
> Opera Software ASA
>



-- 
Peter Beverloo | Software Engineer | beverloo@google.com | +31-6-41000722
Received on Friday, 21 October 2011 10:36:17 GMT

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