Documentation of commands for selecting fonts, as well as those for defining the data-structures used by the selection commands.

For further guidance, two papers may be helpful — “Essential NFSS” by Sebastian Rahtz, written shortly after the appearance of LaTeX2e, and “Font selection in LaTeX” by Walter Schmidt.

Fntguide is part of a set of documentation that also covers new LaTeX 2e commands, class and package writing, typesetting Cyrillic, LaTeX font encodings, configuration options and modification of latex.

The author is The LaTeX Team.