[web2py] Question about 0.py

[devGS]

I saw that object 'settings' is defined at 0.py, but I didn't see any
usage of 'settings'. For instance, in db.py, instead of reusing the
0.py's 'settings', the stings are redefined, even though realize about
some modules that use 'settings' instead of db.py set variables. Can
this point be cleared please? Why is there mail.settings.XYZ = '...'
instead of 'mail.settings.XYZ = settings.XYZ'? Thanks.