make-temp-file?

The exported function HCL:MAKE-TEMP-FILE seems to be useful for
creating temporary files similar to AllegroCL's
MAKE-TEMP-FILE-NAME. Unfortunately, it is not documented, so...

1. I think the second parameter can be used to set the suffix of the
   generated file. Is that true?

2. What's the purpose of the first (RETURN) parameter? If it's NIL the
   function returns a pathname, otherwise it returns a stream. Is that
   the only difference?

3. I can't figure out what the third parameter (SUPPLIED-PATHNAME) is
   for...

4. Is there a way to control which directory is used for temporary
   files?

5. Is there a way (like in AllegroCL) to just return a pathname
   without actually creating the file?

Thanks,
Edi.