This looks very interesting. Thanks. Unfortunately, your test doesn't seem to work here. I added a diag "[", explain($string), "]"; to the end, and I get no output. (i.e., an empty []). Also, I tried adding a "diag '.';" inside the while loop to see how many times it loops, and nothing came out. You're also not reading from $invalid, you need to open my $fh, '<', \$invalid; and then you can read from $fh. But though it now reads one time, the length of the ouput still seems to be zero. I'll see if I can adapt this test to actually have valid utf8 after multiple reads and see what comes of it. Somewhere to start from anyway :-)