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Re: computed values of properties

From: Bjoern Hoehrmann <derhoermi@gmx.net>
Date: Sun, 20 May 2012 01:12:31 +0200
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: "L. David Baron" <dbaron@dbaron.org>, Cameron McCormack <cam@mcc.id.au>, SVG public list <www-svg@w3.org>
Message-ID: <9i9gr75m4m7no7d2sjsarmtmvtdsejukna@hive.bjoern.hoehrmann.de>
* Tab Atkins Jr. wrote:
>On Sat, May 19, 2012 at 4:39 AM, L. David Baron <dbaron@dbaron.org> wrote:
>> On Saturday 2012-05-19 15:02 +1000, Cameron McCormack wrote:
>>> One thing that the SVG 1.1 spec is missing is a definition of how
>>> the computed values of properties are determined.  For example I
>>> notice just now that stroke-width in Gecko will compute an em length
>>> down to a px value and keep percentage values as specified, while in
>>> WebKit and Opera both values are kept as specified.  As I go about
>>> reformatting our property definitions to match CSS specs, I will put
>>> something hopefully reasonable in for the "Computed value" lines,
>>> which I would then appreciate review of.
>>
>> One thing to beware of is that the getComputedStyle() method
>> actually returns used values, which are a significantly different
>> concept from computed values in many cases.
>
>Except when it *does* return the computed value.  It only returns the
>used value for a specific list of 2.1 properties, right?  (Because at
>the time the CSSOM was written, CSS2 had a different definition of
>"computed value" that maps more closely to today's notion of "used
>value".

In actual practise the method currently returns implementation-defined
values, with some consistent behavior among browsers for common uses.
There have been proposals to define it one way or another, but there's
been little interest in putting one of the proposals in a specification,
making a test suite, and updating everything so specification, test
suite, and implementations are properly aligned. I think it would be
better to say it returns something that we have yet to figure out how
to describe (aka, implementation-defined, as above).
-- 
Björn Höhrmann · mailto:bjoern@hoehrmann.de · http://bjoern.hoehrmann.de
Am Badedeich 7 · Telefon: +49(0)160/4415681 · http://www.bjoernsworld.de
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Received on Saturday, 19 May 2012 23:12:59 GMT

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