is a wrapper for a line in a source code file, define by an absolute path
to a source code file and a line number.
A source code file is modeled by a
a specialization of
which serves as the ancestor class for application-specific source file models.
For instance, a specialized model of a Prolog source file would include the locations of clauses.
KahinaSourceFileRegistry is used to cache
KahinaSourceFileModels under absolute path names,
which can lead to a speedup especially if a lot of preprocessing is needed.