W3C home > Mailing lists > Public > www-style@w3.org > January 2000

RE: Units, font sizing, and zoom suggestion for CSS 3

From: Karlsson Kent - keka <keka@im.se>
Date: Thu, 20 Jan 2000 17:47:32 +0100
Message-ID: <C110A2268F8DD111AA1A00805F85E58DA6852A@ntgbg1>
To: www-style <www-style@w3.org>

> -----Original Message-----
> From: Matthew Brealey [mailto:thelawnet@yahoo.com]
> --- Karlsson Kent - keka <keka@im.se> wrote:
> > > >         em - width(!) of a capital M in the current font and size;
> > > >                 this is the historically correct definition of em,
> > > >                 and the definition of em used by TeX; if there is no
> > > >                 M in the font, a suitable approximation is 
> > > calculated.
> > > This is a bad idea - it would ruin all old implementations. 
> > > My wem suggestion is backward-compatible
> > 
> > This is the proper, and traditional, definition of em.  If you for
> > compatibility reasons want to call it wem instead, fine. But then
> > one should strongly deprecate the old CSS em.
> Most definitely not. The em provides fonts and line heights that are in
> proportion, and in particular are essential for accessibility reasons. The
> em is the BEST unit in CSS, not the worst.

I did not say it was bad per se, just that "em" really is
something else.

What you are aiming for is the p unit which I suggested.  The p
(or p or g, or similar) is not my idea by the way; it's been a
more than decade long suggestion from (some) typography quarters.
The problem is that "font size" used to refer to a now obsolete size
of a piece of lead, and does not have any defined relation to the
actual size of glyphs.  The p height refers to actual size of glyphs.
(For the moment ignoring problems that Erik brought up yesterday.)

Of course the p is useful; I've implied nothing else.  So is (true)
em.  Just don't call an unspecified approximation of p an "em".

As for em; I find it better to keep both with traditional definition
*and* modern and widely spread computer typesetting systems like TeX,
where "em" *is* defined as the width of M in the current font.  It is
nice to have the same definition of things across systems; even for
"relative units".  (If it has to me named differently ("wem"?) for a
few CSS versions for compatibility reasons, then so be it.)

As for px; this should simply never be used, possibly with the
exception of use with images.  TeX systems, e.g., work very nicely
without it, including zoomable screen "preview", which is antialisad.

As for pt, dd, pi, ci: my intent is of course that they be
permanently included, but disrecommended, if that is a better word
than "deprecated".

		Kind regards
		/kent k
Received on Thursday, 20 January 2000 11:47:33 UTC

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