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Re: Making pt a non-physical unit

From: Robert O'Callahan <robert@ocallahan.org>
Date: Fri, 15 Jan 2010 09:48:12 +1300
Message-ID: <11e306601001141248n10cca803xf16b801d140433a8@mail.gmail.com>
To: Brad Kemper <brad.kemper@gmail.com>
Cc: www-style <www-style@w3.org>
On Fri, Jan 15, 2010 at 7:38 AM, Brad Kemper <brad.kemper@gmail.com> wrote:

> On Jan 14, 2010, at 2:21 AM, Robert O'Callahan wrote:
> On Thu, Jan 14, 2010 at 2:02 PM, Robert O'Callahan <robert@ocallahan.org>wrote:
>> Our experience is that users do not expect the size of a CSS pixel to be
>> different from one screen pixel by default. They do expect that content such
>> as form controls will be displayed consistently inside the browser and
>> outside it. Therefore attempts to automatically have CSS pixels approximate
>> a particular subtended angle (which we have tried) are not appealing.
> I find myself in complete agreement with you here, Robert (shocking, isn't
> it?).


> And for screen media I think we still have the use-cases of touch
>> interfaces and "life size" diagrams which deserve a "true" unit.
> Let me recapitulate...
> How about the following definition for CSS pixel:
> For print media intended to be read "at hand", a CSS pixel should be
> rendered as 1/96 of an inch.
> Agreed, but for all print media.

Handling exceptionally sized media by treating them as "always having some
default scale" would be OK, but less that optimal from a spec point of view,
IMHO, because it amounts to the spec having nothing to say about what units
should map to in such media, when we could provide useful guidance for
user-agents and authors.

Define "truemm":
> "truemm" is defined to correspond to physical millimeters in all media. For
> extremely small or large output surfaces, or when the physical media
> characteristics are unknown, the user agent may use an approximation.
> I don't want two different kinds of mm.

Do you agree that we need some kind of physical unit? If so, what should it

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Received on Thursday, 14 January 2010 20:48:45 UTC

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