seems i cannot fully understand {/,/usr/local/}/etc/rc.d/*

[Robert Bonomi]

> From owner-freebsd-questions at freebsd.org  Wed Jun 20 03:51:43 2012
> Date: Wed, 20 Jun 2012 10:51:04 +0200 (CEST)
> From: Wojciech Puchar <wojtek at wojtek.tensor.gdynia.pl>
> To: Matthew Seaman <matthew at freebsd.org>
> Cc: freebsd-questions at freebsd.org
> Subject: Re: seems i cannot fully understand {/,/usr/local/}/etc/rc.d/*
>
> >
> > Create a new file in /usr/local/etc/rc.d/precedence with the following
> > contents:
> >
> > #!/bin/sh
> > #
> > # Persuade vboxheadless to start before samba.
> >
> > # PROVIDE: precedence
> > # REQUIRE: vboxheadless
> > # BEFORE: samba
> >
> > :
> >
> > Make it executable.  Note -- the ':' does seem to be necessary.
> >
> thank you for help. I will test it when being on place and could 
> reboot.
>
> But still - do you know why it is necessary?

An explanation written some 80 years ago; 
  'Because that way it will work'.