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Re: [csswg-drafts] [css-values] Traditional absolute length units

From: Christoph Päper via GitHub <sysbot+gh@w3.org>
Date: Fri, 23 Dec 2016 00:01:40 +0000
To: public-css-archive@w3.org
Message-ID: <issue_comment.created-268917416-1482451297-sysbot+gh@w3.org>
I humbly disagree and kindly ask you to be more specific with your 
critique. I believe these units would improve productivity for some 
authors, once widely supported – and therefore should have been 
introduced as early as possible. They are also simpler and cheaper to 
implement than basically every other new CSS feature.

* `m`, `dm`, `mu`|`um` (`my`?) – I don’t even consider these different
 units from `cm` and `mm`. I chose meter and micrometer as the useful 
limits for now, because lengths in most CSS in the wild are ranging 
from less than a millimeter (e.g. underlines) to dozens of centimeters
 (e.g. viewport sizes). If I truly bought @plinss’s SVG map argument, 
I’d have proposed `dam`, `hm` and `km` as well (and probably `sm` and 
`mi`). Beyond these, SI gets ambiguous without case distinction 
* `cc`, `dd` – They were the original reason for opening this issue. 
Although not used much for new designs any more, there’s lots of 
legacy material that c/should be transferred to an open format which 
relies on [css-values], e.g. EPUB. Ciceros also suffer from the same 
problem picas do, namely that those who used them are accustomed to a 
non-decimal notation, but decimal is all that CSS offers conveniently 
→ #378.
* `yd`, `ft` – Personally, I’ll never need, want or use these. I just 
included them because some random British or American guys would 
demand them loudly anyway if `dm` and `m` were to be specced.
* `hd` – At `4in`, this is arguably the most obscure and least useful 
unit I proposed. It’s mostly there as an English equivalent to `dm`. 
I’ll propose anthropometric units separately soon.
* `sx`, `tx` – See @dauwhe’s comment or #378 for why a 1/16-inch unit 
could improve the welcoming culture of CSS. They’re not integer 
multiples of `pt` (but `px`). Writing them as decimal fractions or 
`calc()` expressions feels awkward. Having both, or even the smaller 
`tx` at all, may be overkill, so just `sx` is fine with me, as would 
be changing the name and symbol.
* `twip` – Another unit I wouldn’t use myself, but within an `in`-`pt`
 system they kinda make sense for very small measures like kerning or 
stroke widths. Note that `1px` = `15twip`, i.e. it’s _a_ common 
divisor although not the largest (which would be a “quarter-point”).
* `dot`… – This is not really intended as a unit used by authors, but 
for internal (integer) representation with the minimum expected 
precision, like Te&chi;’s _scaled point_ `sp`. It is based on the 
smallest units currently available (`q`, `px`, `pt`), but could of 
course be changed to the GCD of `twip` and `mu` (which would be 1/25 
of the current definition).

Let’s make CSS homey for more people!

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