Possible problem in CSS techniques document

In the "CSS Techniques for Web Content Accessibility Guidelines 1.0", it 
recommends using 'em' as a relative unit of measurement for heights of 
text and other elements.  This seems fairly broken, as an em is related 
to the width of the 'm' in the current font.  I would have thought it 
better to recommend the use of 'ex' as a unit of height measurement.

If the developer and user have different sets of fonts installed (quite 
common when they are using different platforms), heights in em's can 
give bad results.  For instance, if the developer designs the page for 
use with the Verdana font (which is relatively wide compared to its 
height), and the user's browser picks Helvetica, all heights specified 
in ems will be scaled down compared to the height of the default font.

This is problem is particularly noticable if the developer is trying to 
get a font smaller than the default and uses an em measurement to 
achieve this.  If people want to specify heights/vertical sizes in 
relation to the metrics of the default/current font, they should be 
basing them off a height measurement of the font.

This problem may affect other documents on the site.

James.

-- 
Email: james@daa.com.au
WWW:   http://www.daa.com.au/~james/

Received on Friday, 12 April 2002 08:04:50 UTC