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Re: [css21] The 'inherit' keyword in shorthand properties

From: Anton Prowse <prowse@moonhenge.net>
Date: Mon, 02 Jan 2012 16:17:43 +0100
Message-ID: <4F01CA97.1050603@moonhenge.net>
To: www-style@w3.org
CC: fantasai <fantasai.lists@inkedblade.net>, Øyvind Stenhaug <oyvinds@opera.com>
On 02/01/2012 15:15, Anton Prowse wrote:
> On 02/01/2012 14:59, Anton Prowse wrote:
>> On 14/10/2011 23:31, fantasai wrote:
>>> On 10/13/2011 08:13 AM, Øyvind Stenhaug wrote:
>>>> http://www.w3.org/2011/10/12-css-irc#T16-47-22
>>>>
>>>> "RESOLVED: accept TabAtkins and fantasai's proposal such that inherit
>>>> turns the specified value into the parent's computed value"
>>>>
>>>> I just realized that this doesn't necessarily make any sense for
>>>> shorthand properties. In fact, most of chapter 6 seems to
>>>> operate under an unstated assumption that each declaration setting a
>>>> shorthand has been converted to equivalent declarations
>>>> for the corresponding longhand properties.
>>>>
>>>> There is a sentence about how declaring a shorthand to be !important
>>>> is equivalent to declaring all of its sub-properties to
>>>> be !important. Probably there should be similar wording for 'inherit'.
>>>
>>> I suggest instead stating that unstated assumption so that this all works
>>> and we don't have to work out every missing detail.
>>
>> Surely this is just a special case of setting /any/ value on a shorthand
>> property? If it's not clear from 1.4.3 (Shorthand properties)[1] that
>> the mechanism works like that then I think we should solve that more
>> general issue instead. ("!important" is different because it's not a
>> value.)
>>
>> The problem that Øyvind raises with regards to the change proposal[2,3]
>> is part of the wider problem that value assignment on shorthand
>> properties is not well-defined.[4] The proposal above doesn't solve that
>> problem even in the case that Øyvind describes.
>>
>> [1] http://www.w3.org/TR/CSS21/about.html#shorthand
>> [2] http://lists.w3.org/Archives/Public/www-style/2011Oct/0482.html
>> [3] http://www.w3.org/Style/css2-updates/REC-CSS2-20110607-errata.html
>> [4] https://www.w3.org/Bugs/Public/show_bug.cgi?id=15384
>>
> Sorry, please ignore me; my claim is incorrect, and I do think the
> behaviour of 'inherit' on shorthands needs clearer treatment.

I take it back; I believe my claim and comments *do* stand, and that 
this problem is just a special case of the fact that value assignment on 
shorthand properties is not well-defined.  (Apologies for my wavering; I 
blame it on the abrupt end of the holiday season!)

It's often the lack of an obvious /computed/ value for shorthand 
properties that alert us to the wider problem of value assignment on 
shorthand properties, but in this case we see the lack of a /specified/ 
value for shorthand properties.  The proposal wouldn't provide this value.

Unfortunately, I can't see that it would be any easier to solve this 
special case with an alternative proposal than it would be to solve the 
general problem.  Nonetheless, I've tracked this issue separately at 
https://www.w3.org/Bugs/Public/show_bug.cgi?id=15387 with references to 
the general problem.

Cheers,
Anton Prowse
http://dev.moonhenge.net
Received on Monday, 2 January 2012 15:18:15 GMT

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