bug#3138: 23.0.92; doc of ediff-patch-file

C-h f ediff-patch-file -> 
 
 (ediff-patch-file &optional ARG PATCH-BUF)
 

 Run Ediff by patching SOURCE-FILENAME.
 If optional PATCH-BUF is given, use the patch in that buffer
 and don't ask the user.
 If prefix argument, then: if even argument, assume that the patch is in a
 buffer. If odd -- assume it is in a file.
 

So what is SOURCE-FILENAME?
 
 
 
In GNU Emacs 23.0.92.1 (i386-mingw-nt5.1.2600)
 of 2009-03-30 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'