[plt-scheme] determining requires

Given a particular help page, like for example:

drscheme:unit:open-drscheme-window in DrScheme Tools Functions

is there a specific way that one can determine the require statement
you should use?  Like for this one, I did some greps through the
source code tree I found:

collects/drscheme/private/unit.ss has a define like that,so i try:

(require (lib "private/unit.ss" "drscheme"))

> (drscheme:unit:open-drscheme-window)
. reference to undefined identifier: drscheme:unit:open-drscheme-window
> (drscheme:open-drscheme-window)
. reference to undefined identifier: drscheme:open-drscheme-window
> (unit:open-drscheme-window)
. reference to undefined identifier: unit:open-drscheme-window
> (open-drscheme-window)
reference to undefined identifier: open-drscheme-window

i found another file that requires unit, so tried:
  (require (lib "private/drsig.ss" "drscheme"))

and got the same thing, then found a file that requires drsig.ss, so tried:

 (require (lib "tool.ss" "drscheme"))

and got the same thing.  How do i find the correct requires to import
something referenced in the help?

 Corey