xinstall vs. file copy & file mkdir

[Ryan Schmidt]

What's the difference between "xinstall" and "file copy" and "copy"?  
Here's what I've found:

- xinstall has the -W option so you can say "xinstall -W src a b c d  
dst" to copy a whole bunch of named files from src to dst. It doesn't  
look like file copy can do that.
- file copy can copy directories. It doesn't look like xinstall can  
do that.
- file copy preserves modification dates. xinstall does not.
- copy is the same as file copy.

What's the difference between "xinstall -d" and "file mkdir"? I don't  
know. And if there's a reason to use "file mkdir", should there be an  
alias "mkdir" for it?

The guide should explain these differences, and when one should  
prefer one option over the other.