perl -MXML::Twig -l -MEncode -e'print Encode::is_utf8( XML::Twig->nparse( "<d>foo</d>")->root->text)'
perl -MXML::Twig -l -MEncode -e'print Encode::is_utf8( XML::Twig->nparse( qq{<?xml version="1.0" encoding="ISO-8859-1"?><d>foo</d>})->root->text)'