*.cls
while package
files are called *.sty
. Thus we find that the LaTeX
standard article class is represented on disc by a file called
article.cls, while the footmisc package (which
refines article’s definition of footnotes) is represented on
disc by a file called footmisc.sty.
The user defines the class of his document with the
\
documentclass
command (typically the first command in a
document), and loads packages with the \
usepackage
command. A
document may have several \
usepackage
commands, but it may have
only one \
documentclass
command. (Note that there are
programming-interface versions of both commands, since a class may
choose to load another class to refine its capabilities, and both
classes and packages may choose to load other packages.)
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=clsvpkg