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Re: What's an em

From: David Lemon <typenerd@slip.net>
Date: Wed, 2 Feb 2000 11:59:18 -0500 (EST)
Message-Id: <l03130304b4be0c15f574@[207.171.234.10]>
To: www-style@w3.org, www-font@w3.org
At 9:47 PM +0100 2/1/00, Karlsson Kent - keka wrote:
> (Opentype?) focuses on a measure
> (descender to ascender height) that is *NOT* of major interest
> to the font USER.

The nominal type body height is definitely of interest if the user is going
to set more than one line.

At 2:03 PM -0800 2/1/00, Erik van der Poel wrote:
> What, exactly, is the OpenType "ascender" and "descender"? Does the
> ascender refer to the tops of the letters bdfhkl? Or does ascender refer
> to the accents above the capital letters?

It's currently unspecified (except, as Jelle Bosma pointed out, that
ascender + descender + line gap = recommended minimum line spacing). What I
mentioned before is that Adobe is using the ascender and descender values
to explicitly record the em height relative to the baseline, and
recommending this practice to others. We'll see whether this makes it into
the OpenType spec.

> This would require all font vendors to update their fonts if
> they want users to be able to use them on the Web, where unpredictable
> substitution occurs. Many vendors may not care about the Web, and may
> leave their old fonts as they are.

I can think of only one obscure company which might "not care about the
Web". However, fonts are not like other software: Users don't want to
upgrade, so virtually every Type 1 or TrueType font that was ever sold is
still in use. I'm still getting complaints about font glitches that were
fixed more than a decade ago. If CSS doesn't work with today's fonts, it's
going to have big problems.

> Or they may come up with new designs
> specifically for the Web. Doesn't Adobe have particular fonts for the
> Web, even with the word "Web" in their names?

While there can be some value in making fonts which are optimized for
on-screen use (whether Verdana or Minion Web), even the wildest display
designs are going to be used, so all fonts need to work as well as
possible. Certainly Adobe doesn't think only the "Web Type" collection
should be used on screens.

- David Lemon
Received on Thursday, 3 February 2000 10:26:36 GMT

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