Text::Locus provides a class for representing locations in text files.
A simple location consists of file name and line number, e.g. file:10.
In its more complex form, the location represents a text fragment
spanning several lines, such as file:10-45.  Such a fragment need not
be contiguous, a valid location can also look like this:
file:10-35,40-48.  Moreover, it can span multiple files as well:
foo:10-35,40-48;bar:15,18.