$ perl -MEncode -MJSON -e " print JSON->new->utf8(0)->pretty(1)->encode([ decode 'utf8', qq{\xFA\xFG} ]); "
Wide character in print at -e line 1.
[
   "�\u000fG"
]

$ perl -MEncode -MJSON -e " print JSON->new->ascii(1)->pretty(1)->encode([ decode 'utf8', qq{\xFA\xFG} ]); "
[
   "\ufffd\u000fG"
]