the link() function, as it has not much description on perldoc -f

I agree that perldoc -f link could use a little more information. Perhaps a monk with more familiarity with the function could enhance the documentation via perlbug.

So, then I googled "perl link", and I found this http://www.tutorialspoint.com/perl/perl_link.htm, which mentions perldoc -f symlink. I realize this does not directly answer any of your questions, but maybe it is of some use.