Cascading Style Sheets - HTML and XHTML: The Definitive Guide - page 469

interested authors should refer to appropriate documentation for the
Panose-1 system for more information.
The stemv and stemh descriptors define the thickness, in ems, of the ver-
tical and horizontal strokes of the font. Similarly, the cap-height and x-
height descriptors define the height of the upper- and lowercase glyphs
in the font. Finally, the ascent and descent descriptors define the font's
maximum height and depth. If you use any of these descriptors, you
must also specify the units-per-em descriptor.
The slope descriptor defines the slope of the vertical stroke of the font.
This is important for matching italic and oblique versions of a font.
The baseline, centerline, mathline , and topline descriptors define the
conventional baseline, center baseline, mathematical baseline, and top
baseline of the font. All accept a numeric value expressed in ems. All
require that you specify the units-per-em descriptor, too.
The bbox descriptor accepts exactly two coordinate (X, Y) pairs, specify-
ing the lower-left and upper-right corners of the font's bounding box.
The bbox descriptor is important if the browser chooses to synthesize a
font based on this font. By specifying the size of the bounding box, you
ensure that the synthesized font occupies the same space as the desired
one.
The widths descriptor accepts a comma-separated list of Unicode
ranges, followed by space-separated values which define the widths of
the characters in the indicated range. If you supply one value for a
range, all the characters in that range have the same width. Multiple
values are assigned to successive characters in a range. Like the bbox
descriptor, the widths descriptor is used to ensure good fidelity between
a synthesized font and its requested counterpart.
Finally, the optional definitions-src descriptor provides the URL of a
file that contains all of the descriptors for a font. This is handy if you
need to define a font in great detail. Instead of including the lengthy
descriptors in each document or stylesheet that uses the font, you