php 让浏览器格式化显示XML

header("Content-type: application/xml");

$Dom = new \DOMDocument('1.0', 'utf-8');
$paper = $Dom->createElement('paper');
$Dom->appendChild($paper);

$exercises =  $Dom->createElement('exercises');
$exercises->setAttribute('id','1');
$exercises->setAttribute('type','1');
$exercises->setAttribute('answer','1');
$paper->appendChild($exercises);

$title =  $Dom->createElement('title');
$title->setAttribute('label','1');
$title->setAttribute('mapsrc','1');
$title->setAttribute('soundsrc','1');
$exercises->appendChild($title);

$option =  $Dom->createElement('option');
$option->setAttribute('id','1');
$option->setAttribute('label','1');
$option->setAttribute('mapsrc','1');
$option->setAttribute('soundsrc','1');
$exercises->appendChild($option);

header("Content-type: application/xml");
echo  $Dom->saveXml(); exit;