That function is used to translate a filename that’s part of a package.
Currently it’s not in use but I plan to allow some kind of packaging support, from at least to ways:
Packaging is tricky, especially because the system migth handle the developement
time (the files are on the filesystem) and the release
time (the files are packaged).
Using this function will allow to handle this cases and optionnaly to be independant from the packing (in the ideal).
I’m currently far from this point, but once done you will see the result here