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Re: [CSS21] Issue 149 - px vs. pt

From: Henri Sivonen <hsivonen@iki.fi>
Date: Thu, 1 Jul 2010 14:31:14 +0300
Cc: "www-style@w3.org" <www-style@w3.org>
Message-Id: <968E7047-B1F4-4D1B-82C9-845DF8E5EE1D@iki.fi>
To: fantasai <fantasai.lists@inkedblade.net>
On Jun 17, 2010, at 04:32, fantasai wrote:

> | Absolute length units are only mainly useful when the physical
> | properties of the output medium are output environment is known.
> | The absolute units are:
> |
> |    * in: inches  1 inch is equal to 2.54 centimeters.
> |    * cm: centimeters
> |    * mm: millimeters
> |    * pt: points  the points used by CSS 2.1 are equal to 1/72nd
> |                   of an inch.
> |    * pc: picas  1 pica is equal to 12 points.
> |    * pt: pixel units  1 pixel unit is equal to 0.75 points.

I think the new text doesn't make it clear enough that these units are all defined as a constant multiplier times px. Also, the term "absolute" is misleading.

I suggest naming these something like "pseudo-physical units" (to make it clear that their relationship to the physical units of the same names is pseudo) and replacing the first paragraph above the list with something like "Pseudo-physical units are named after well-known physical length units. They exist in CSS for legacy reasons and are defined in terms of the px unit. The pseudo-physical units are:"

And then defining "in" as 96px and defining "cm" as 1/2.54 in.

-- 
Henri Sivonen
hsivonen@iki.fi
http://hsivonen.iki.fi/
Received on Thursday, 1 July 2010 11:31:53 GMT

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