Perl has two pseudo-constants describing the current location in your source
 code, __FILE__ and __LINE__. Dir::Self adds __DIR__, which expands to the
 directory your source file is in, as an absolute pathname.
 .
 This is useful if your code wants to access files in the same directory, like
 helper modules or configuration data. This is a bit like FindBin except it's
 not limited to the main program, i.e. you can also use it in modules. And it
 actually works.