23.0.60; doc of dired-read-shell-command

[Drew Adams]

1. The dired-x.el version of the function has this doc string:
 
"Read a dired shell command prompting with PROMPT (using read-string).
ARG is the prefix arg and may be used to indicate in the prompt which
  files are affected.
This is an extra function so that you can redefine it."
 
What is that last line supposed to mean? What does "extra function"
mean? And why is dired-x.el permitted to redefine the function?
 
2. The dired-aux.el version of the function has no doc string. It has
a comment that says almost the same thing, but no doc string.
 
These descriptions and the intention regarding redefinition are not
clear. At the very least, both functions should have doc strings, and
the doc strings should be clear.
 

In GNU Emacs 23.0.60.1 (i386-mingw-nt5.1.2600)
 of 2008-04-04 on LENNART-69DE564
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --no-opt --cflags -Ic:/g/include
-fno-crossjumping'