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Re: [css-multicol] column-width bound (>0) is illegal

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 15 Oct 2013 11:50:50 -0700
Message-ID: <CAAWBYDDKP__MaXnf+2DbxSjjnC1muB91brzz=2Kr97+W9y9jYA@mail.gmail.com>
To: Gérard Talbot <www-style@gtalbot.org>
Cc: www-style list <www-style@w3.org>
On Tue, Oct 15, 2013 at 11:14 AM, Gérard Talbot <www-style@gtalbot.org> wrote:
> Le 2013-10-15 11:38, Tab Atkins Jr. a écrit :
>> Per our design patterns for CSS properties (apparently not written
>> down anywhere, unfortunately*), we don't use open continuous
>> intervals
> I've read your message several times and I'm not sure I understand it... and
> what you may mean with open continuous intervals.

Apologies, these are standard mathematical terms in English.

"Open" and "closed" intervals refer to whether the endpoint is
included in the interval or not.  These may also be called "exclusive"
and "inclusive" intervals.

"Continuous" was used to mean the opposite of "discrete".  The CSS
<number> type is continuous - you can subdivide it as finely as you
wish (though there are of course implementation-defined limits on the
precision you can achieve), while the CSS <integer> type is discrete -
there is a minimum distance between consecutive values.

>> , because then whether something is valid or invalid depends
>> on unpredictable and UA-specific rounding behavior.
>> However, 'column-width' states that its value must be a <length>
>> greater than zero.  This violates that constraint.
> "
> A length is a dimension. (...)
> A dimension is a number immediately followed by a unit identifier. (...)
> A number is either an <integer> or zero or more decimal digits followed by a
> dot (.) followed by one or more decimal digits.
> "
> http://www.w3.org/TR/css3-values/#lengths
> Are you saying that column-width must not be using a real number (eg
> column-width: 12.5px;)?

No.  You're focusing on the wrong part of that sentence - the relevant
part is the "greater than zero", which means that 0.1, 0.01, 0.001,
0.0000000...01 are all technically valid, but 0 is invalid.  The issue
is that, in reality, at some point rounding or precision limits kick
in, and a value that is "technically" greater than zero gets converted
to zero, thus making the declaration invalid.  Because this point is
impossible to predict ahead of time, and may differ between UAs and
even within a single UA over time, it is bad to make the validity of
the property depend on it.

>> I suggest that we instead state that there is a minimum size for
>> columns (1px? ua-specific?), and that values less than this minimum
>> are clamped to the minimum.  Values less than zero are still invalid,
>> as they're nonsensical.
> You say minimum is 1. The spec says greater than 0. Isn't those equivalent?

No.  There are an infinity of values between 0 and 1.

> http://test.csswg.org/suites/css3-multicol/nightly-unstable/html4/multicol-count-large-001.htm
> http://test.csswg.org/suites/css3-multicol/nightly-unstable/html4/multicol-count-large-002.htm
> In both these tests, the column-count is 1000 while the width of the
> multi-column container is 192px. Is your message related somehow to these 2
> tests ?

Not really, no.  Those are dealing with large column-count values.
This message is about small column-width values.

> please put the text "css3-multicol" in the subject and not "css-multicol" in
> the future.

Both are used in practice, and specs advocate a mixture of them.
Since "cssN-foo" is no longer the shortname pattern in use for specs,
it would be odd to continue using it for the subject indicator.

Received on Tuesday, 15 October 2013 18:51:37 UTC

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