A mod_info represents an existing, installed module and its runtime
physical location (usually in the file system).
mod_info(spec, source_path)pkg_info(spec)
mod_info and pkg_info return a structure representing
the module/package information for the given specification/source location.
a mod_spec or pkg_spec (for mod_info and
pkg_info, respectively)
character string full path to the physical module location.