$ perl -MDevel::Peek -MEncode=_utf8_on,_utf8_off -e'_utf8_on( $x="\200\201" ); Dump $x; _utf8_off $x; Dump $x'
  PV = 0x81651e8 [UTF8 "\x{1}@"]
  PV = 0x81651e8 "\200\201"\0