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Re: [css3-values][css-variables] definition of <value>

From: Kang-Hao (Kenny) Lu <kennyluck@csail.mit.edu>
Date: Tue, 10 Jul 2012 08:57:50 +0800
Message-ID: <4FFB7E0E.9050106@csail.mit.edu>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
CC: WWW Style <www-style@w3.org>
(12/07/10 4:34), Tab Atkins Jr. wrote:
>> A formal syntax with ambiguous syntax should generally be avoided. An
>> ambiguous syntax would make a parser generator give a warning, which is
>> not a good thing.
>>
>> I am talking about this line:
>>
>>   toggle( <value># )
>>
>> , which is ambiguous if you don't normatively say <value> can't contain
>> comma.
> 
> I've altered the definition of <value> to explicitly disallow
> top-level commas.  Is the spec acceptable now?

Yes, thanks.

>>> Functions always split their arguments on commas.
>>> "toggle(blue, white)" is two arguments, not a single "blue, white"
>>> argument.  The only exception is when we define that a trailing
>>> argument can contain commas itself (such as in attr()),
>>
>> So the prose has
>>
>>   # The optional <fallback> argument represents a fallback value, which
>>   # is used if the named attribute is missing, or its value cannot be
>>   # parsed into the given type or is invalid/out-of-range for the
>>   # property. If it's absent, the default value for the given
>>   # <type-or-unit> (from the list below) is implied.
>>
>> which doesn't explicitly say <fallback> can contain comma.
> 
> It's unnecessary to explicitly say that, any more than we need to
> explicitly say it can contain spaces.

Before toggle() mentions that <value> can't contain comma, it's just not
possibile to tell why <fallback> can contain comma and <value> can't,
without looking at the note, which isn't part of the normative spec.

Now that there a normative sentence backing up this difference, it's
clearer now.

But in general, we seem to have very different criteria about what makes
a "definition". This is what happened:

1. You said "the only exception is when we define that a trailing
argument can contain commas itself (such as in attr())"
2. Since you used the word "define" instead of "say", I expected that I
could find a normative sentence about this in the description of attr().
3. I found nothing, and hence the complaint.

I would encourage CSS specs to go the side where everything is
well-defined and reading it is as enjoyable as reading the HTML spec:
full of definitions, hyperlinks and step-by-step algorithmic procedures.
css3-syntax is close to this but css3-values is not.


Cheers,
Kenny
Received on Tuesday, 10 July 2012 00:58:16 GMT

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