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

From: <JOrendorff@ixl.com>
Date: Tue, 25 Jan 2000 21:14:33 -0500
Message-ID: <CD8E2CDBC6D0D111ACB900805FBBD97E02630144@mem-131.ixl.com>
To: www-style@w3.org
The current SVG working draft is a little more explicit about
'font-size':

    "This property refers to the size of the font from baseline to
    baseline when multiple lines of text are set solid in a multiline
    layout environment." [1]

For computerized, scalable fonts, I think it's reasonable to say
that this means the minimum recommended baseline-to-baseline distance--
recommended, that is, by the font itself.  I feel sure that this is the
intended meaning of 'font-size' in CSS2.  Given what the spec says about
'em', 'font-size', and 'line-height', this is the only reasonable
interpretation.  Changing the definition for CSS3 is a bad idea, too.

Suppose we decouple 'em' from 'font-size' and redefine 'em' to mean
"the width of an M (or similarly square) glyph in the relevant font."
Then 'line-height: 1em' will cause lines to overlap.

Suppose we keep 'em' and 'font-size' equivalent and define them both
to mean "the width of an M glyph".  This is even worse.  'font-weight:
bold' would no longer widen the characters but instead reduce their
height; the same with 'font-stretch: expanded'.

I oppose changing the rules now.  It would only cause futher disparity
among the implementations-- the last thing we need.  The proportion of
pedantic typesetters in CSS's target audience is not high enough to
justify the change.  ;-)

This being said, 'font-size' and 'em' should be more carefully defined
in CSS3 (and in SVG for that matter).  In SVG Fonts, the relationship
between 'font-size'[1] and 'units-per-em'[2] should be clarified.

[1] http://www.w3.org/TR/SVG/text.html#FontSizeProperty
[2] http://www.w3.org/TR/SVG/fonts.html#FontElementUnitsPerEmAttribute

-- 
Jason Orendorff
Received on Tuesday, 25 January 2000 21:15:09 GMT

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