$ perl -MStorable=freeze -e'
   utf8::upgrade( $_="abc\x{80}def" );
   print freeze(\$_);
' | od -c
0000000 004  \a 004   1   2   3   4 004 004 004  \b 027  \b   a   b   c
0000020 302 200   d   e   f
0000025

$ perl -MStorable=freeze -e'
   utf8::downgrade( $_="abc\x{80}def" );
   print freeze(\$_);
' | od -c
0000000 004  \a 004   1   2   3   4 004 004 004  \b  \n  \a   a   b   c
0000020 200   d   e   f
0000024