- From: Alan Gresley <alan@css-class.com>
- Date: Thu, 29 Sep 2011 14:41:51 +1000
- To: Boris Zbarsky <bzbarsky@MIT.EDU>
- CC: public-css-testsuite@w3.org

On 29/09/2011 6:23 AM, Boris Zbarsky wrote: > 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. This is what I would expected but the wording in the spec is a surprise to me. >> 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. Testing. -0 = 0 = +0 100px = +100px My question is why implementations would allow something like margin-left: +100px in the first place? -100px is a negative number but does not equal 100px or +100px. >> 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)? I hope not since that would mean including all positive and negative numbers to infinity with a extra subset (or sub equation) for all negative numbers like so. -100px (+100px x 2) == 100px == +100px or -nIDENT (+nIDENT x 2) == nIDENT == +nIDENT > 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".... > > -Boris I would recommend removing all of this. # Both integers and real numbers may be preceded by # a "-" or "+" to indicate the sign. -0 is equivalent # to 0 and is not a negative number. And replacing it with this: | All negative integers and negative real numbers are | preceded by a "-" to indicate the sign. All other | integers and real numbers have no sign. I see not reason for the '+' sign and zero is just zero. http://en.wikipedia.org/wiki/0_(number) -- Alan Gresley http://css-3d.org/ http://css-class.com/

Received on Thursday, 29 September 2011 04:42:32 UTC