I don't know where to look for this in the docs, but isa handles inheritance, whereas ref does not. For example: 
package A;

sub new {
    my $c = shift;
    $c = ref $c || $c;
    bless {}, $c;
}

package B;

@ISA=qw(A);
sub new {
    my $c = shift;
    $c = ref $c || $c;
    bless {}, $c;
}

package main;

my $b = new B;
print "b isa A = ", $b->isa('A'), "\n";
print "ref b = ", ref($b), "\n";

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/s

In reply to Re: semantics differences, &ref and &UNIVERSAL::isa() by educated_foo
in thread semantics differences, &ref and &UNIVERSAL::isa() by dakedesu

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