Font Substitution
The fontconfig library performs font substitution
when either entire fonts, or individual characters, are not present. If the
system needs to display a font that is not available, fontconfig attempts to display another, similar font. For example, if a web
page requests to display the Verdana font, and that font is not installed
on the system, fontconfig displays a similar font, such
as Helvetica. The list of similar fonts is defined in the /etc/fonts/fonts.conf file.
If the system needs to display a character that is not present in the
selected font, fontconfig attempts to display the character
in another, similar font. For example, you might select Bitstream Vera Sans
as the font for the Text Editor application. The Bitstream Vera font family
does not include Cyrillic characters. If you open a document which contains
a Cyrillic character, Text Editor uses a similar font that includes Cyrillic
characters to display the character.
The fontconfig library also defines aliases for fonts,
for example, serif, sans-serif, and monospace. When you select one of the aliases for a font, the system
uses the first font that is defined for that alias in the /etc/fonts/fonts.conf.