my $s = 'ABCDE';
print substr($s,0,2)='',$/;    # EXPECT '', GET 'cd'?
print substr($s,0,2)='foo',$/; # EXPECT 'foo', GET 'fo'?

##</code><code>##

my $s = 'ABCDE';
print $s='',$/;                # EXPECT ''
print $s='foo',$/;             # EXPECT 'foo'