W3C home > Mailing lists > Public > public-css-testsuite@w3.org > September 2011

Re: [CSS3-mediaqueries]: Invalid test cases in test suite

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Fri, 30 Sep 2011 01:16:02 -0400
Message-ID: <4E855092.5060702@mit.edu>
To: Arron Eicholz <Arron.Eicholz@microsoft.com>
CC: "public-css-testsuite@w3.org" <public-css-testsuite@w3.org>
On 9/29/11 12:22 PM, Arron Eicholz wrote:
> But what is a real number to CSS?

The same thing they are to the rest of the world.  The unique totally 
ordered complete field.  There are various other definitions, but they 
all give an equivalent structure.

> There is no reference from the CSS spec to go off of for real numbers.

OK, so you just want a normative reference for the term "real number"?

> You are correct that we say real numbers but the spec doesn't say if 0 is included in positive or negative numbers

That's because in the context of real numbers positive and negative have 
standard definitions that exclude 0.

http://en.wikipedia.org/wiki/Positive_number#Sign_of_zero is worth 
reading here if you care.

>> Typical fairly equivalent definitions of 0 would then include:
>> * The smallest element of the subset of the real numbers called the
>>     "Natura numbers".
>> * The additive identity in the field structure of the real numbers.
>> * "That thing defined in the first Peano axiom."
> You are just reinforcing my point. This definition basically says that 0 is a real number


> and most likely would be a positive number.

Where the heck is that last part coming from?  Seriously, what 
definition of "positive" are you using here that just happens to differ 
from every single standard definition?

Do we need to define that the digit '1' when used in the spec is meant 
to represent the same thing as '1' usually in the context of the real 
numbers (that is, the multiplicative identity)?

How much of the axiomatic structure of the reals does the spec need to 
include, either directly or by reference, to make you happy, exactly?

>> I have no idea what you're talking about here.
> I am talking about the problem that 0 and +0 are not explicitly stating that they are or are not positive numbers.
> We are explicit about -0 why not also be explicit about +0 and 0?

OK, I have no problem with that as an informative note, as I said.

Should we be explicit that 1 is a positive number? 2? 3? Others?

>> We can explicitly say that -0 == 0 == +0, of course, as an informative note or
>> something, if you think that makes things clearer for people who are
>> unfamiliar with the term "real number"....
> I am not disagreeing with you on the basis that I don't understand what you are saying. What I am saying that the spec needs to be more explicit or have more references. We seem to be lacking both at this time. Personally I think we just need to be more explicit and add the following text:
> -0 is equivalent to 0 and is not a negative number. +0 is equivalent to 0 and is not a positive number. 0 is neither positive nor negative number.

What I don't understand is why we're worrying about 0 more here than 
about any other real number.  Why doesn't the spec need to be explicit 
that 1 is positive?

Received on Friday, 30 September 2011 05:16:41 UTC

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