xinstall vs. file copy & file mkdir

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.