What is the purpose of the editor notations at the base of source files?

[r cs]

In many files such as ~/test/lib/misc.l there is a notation at the bottom
of the source file "# vi:et:ts=3:sw=3".  What does it do and how does one
leverage it?

Thanks,
rcs

-- 
*Níl aon tinteán mar do thinteán féin. *[Irish Gaelic]
(There is no fireside like your own fireside.)