Packets with headers and trailers split on two lines:

Non-packet whose header contains carriage return:
<?xpacket begin='' id='W5M0MpCehiHzreSzNTczkc9d'
bogusattr="zyz"?><?xpacket end='w'?>

Valid header, invalid trailer containing carriage return:
+++hG<?xpacket begin='' id='W5M0MpCehiHzreSzNTczkc9d'?><?xpacket end='w'
bogutattr="xox"?>

Valid trailer to match valid header above:
<?xpacket end='w'?>---tG