emit($1), next if m/\G([^<>&]+/gc;
  emit($1), next if m/\G(&\w+;)/gc;
  emit("&lt;"), next if m/\G<(?!<)/gc;
  # handle potentially valid REs here
  emit("&lt;"), next if m/\G</gc;
  emit("&gt;"), next if m/\G>/gc;