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

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Wed, 28 Sep 2011 16:23:45 -0400
Message-ID: <4E838251.1040708@mit.edu>
To: public-css-testsuite@w3.org
On 9/28/11 4:13 PM, Arron Eicholz wrote:
> CSS 2.1 still doesn't cover 0 exactly. What is 0?

The CSS 2.1 spec says its numbers are real numbers.

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."

and so forth.  As in, this is the zero you learned about in grade 
school; nothing magic about it.

> Since -0 is equivalent to 0 and is not a negative number that completely explains -0. It does not however explicitly explain what 0 or +0 is or isn't. We must therefore draw the conclusion that +0 is positive and 0 can be both positive and negative.

I have no idea what you're talking about here.

> We need explicit text explaining this

How much more explicit than "these are real numbers" can you get?  Or do 
you want the CSS spec to include some subset of the field axioms for the 
reals, enough to prove that +0 == 0 == -0 (using the usual definitions 
of unary + and - for the reals, which would likewise need to be included 
in the CSS spec)?

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"....

Received on Wednesday, 28 September 2011 20:24:23 UTC

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