The underscore character _
is ordinarily used in TeX to indicate a
subscript in maths mode; if you type _
in the course of ordinary
text, TeX will complain. If you're writing a document which will
contain a large number of underscore characters, the prospect of
typing \_
(or, worse, \textunderscore
) for every one of them
will daunt most ordinary people.
Moderately skilled macro programmers can readily generate a quick hack
to permit typing _
to mean 'text underscore'. However, the code
is somewhat tricky, and more importantly there are significant
points where it's easy to get it wrong. There is therefore a package
underscore which provides a general solution to this
requirement.