How can I get Perl's ref() function to return REF, IO, and LVALUE?

Question

The documentation for ref() mentions several possible return values. I understand most of them, but not REF, IO, and LVALUE. How would

Answer 1

1. LVALUE

   perl5.8 -e '{$a = "aaa"; $b = \substr($a, 0, 2); print "$$b\n"; print ref($b)."\n"}'

   aa

   LVALUE

   This one is explained in perldoc -f ref

2. REF

   perl5.8 -e '{$a = "aaa"; $b = \\$a; print ref($b)."\n"}'

   REF

   It's basically a reference to a value that is itself a reference. Probably would have been better to do $b = \$a; $c = \$b; print ref($c)