question about grub-install

[Paul E Condon <pecondon@mesanetworks.net>]

I am frustrated by a detail of the man page for grub-install.
I suppose I could answer my question by a little experimentation
but I hesitate to be constantly rewriting the MBR of my primary
disk when I might instead get the answer by asking here. Asking
here is far less dangerous than miswriting my disk's MBR. ;-)

I quote a few lines from the man page concerning an option:

--root-directory=DIR
       install  GRUB images under the directory DIR instead of the root
       directory

Is the default for DIR actually '/' ? It seems to behave as if the
default is '/boot'. Or is DIR the place that grub-install starts a
search for boot?

And why does it say 
"install  GRUB images under the directory ..."? 

Isn't it installing something in the MBR? Not is a directory? Or do I
*really* misunderstand what grub-install does? What is a "GRUB image"?
Or am I parsing this incorrectly?

More generally; Does grub-install have a search function? If so, what
is it that grub-install looks for? How does it know that it has found
what it is looking for? How deeply does it search in the directory
tree? When does it decide to stop searching and go with whatever it
has already found? "info grub-install" is no help. It seems to be
identical to the man page. Lastly, will the answers change for grub2?

TIA
-- 
Paul E Condon           
pecondon@mesanetworks.net