(Mythical?) 'Linux setup area' parameters for initrd

[Harmon S. Nine]

Grub help gives the following description of the "initrd" command for 
loading initial ramdisks:

grub> help initrd
initrd: initrd FILE [ARG ...]
   Load an initial ramdisk FILE for a Linux format boot image and
   set the appropriate parameters in the Linux setup area in memory.


I can't seem to find any information on the 'Linux setup area' mentioned 
in this help, nor anything about 'appropriate parameters' for said area, 
or how to set such parameters for this command.

Searching the web has yielded no information beyond what is shown in 
this "help" message.

Can someone describe what the 'Linux setup area' is, what the valid 
parameters for it are, and how to specify them in the grub initrd command?

TIA

-- Harmon