The package keeps track of whether a command defined in a
document preamble is actually used somewhere in the document.
After the package is loaded in the preamble of a document, all
\newcommand (and similar command definitions) between that
point and the beginning of the document will be marked for
logging. At the end of the document a report of command usage
will be printed in the TeX log, for example: "mdash was used on
line 25"; "ndash was never used".
