方法一：
$xmlpath = \'manual.xml\';
$dom = new DOMDocument(\'1.0\',\'utf-8\');
//注意下面两行，作用是格式化XML格式，如缩进等
$dom->preserveWhiteSpace = false;
$dom->formatOutput = true;

if (!file_exists($xmlpath)) {//判断xml文件是否存在
$manuals = $dom->createElement(\'manuals\');
$manual = $dom->createElement(\'manual\');

$manual->setAttribute("manuName", "$manuName" );
$manual->setAttribute("manuNameEN", "$manuNameEN" );
$manual->setAttribute("manuFolder", "$manuFolder" );

$manuals->appendChild($manual);
$dom->appendChild($manuals);
echo $dom->save($xmlpath);
}
else {
$dom->load($xmlpath);
$manuals = $dom->getElementsByTagName(\'manuals\');//获取manuals节点
$manual = $dom->createElement(\'manual\');//创建manual元素节点

$manual->setAttribute("manuName", "$manuName" );
$manual->setAttribute("manuNameEN", "$manuNameEN" );
$manual->setAttribute("manuFolder", "$manuFolder" );
$manuals->item(0)->appendChild($manual);//在名字为manuals的元素节点中的第一个元素后插入
echo $dom->save($xmlpath);
}
生成的XML文件格式如下：
<?xml version="1.0" encoding="utf-8"?>
<manuals>
<manual manuName="Javascript手册" manuNameEN="javascript" manuFolder="js/"/>
<manual manuName="ASP" manuNameEN="ASP" manuFolder="asp/"/>
<manual manuName="PHP" manuNameEN="PHP" manuFolder="php/"/>
</manuals>

另一方法（只是XML格式不同）
$xmlpath = \'manual.xml\';
$dom = new DOMDocument(\'1.0\',\'utf-8\');
//注意下面两行，作用是格式化XML格式，如缩进等
$dom->preserveWhiteSpace = false;
$dom->formatOutput = true;

if (!file_exists($xmlpath)) {//判断xml文件是否存在
$manuals = $dom->createElement(\'manuals\');
$manual = $dom->createElement(\'manual\');

$manuName = $dom->createElement(\'manuName\',$manuName);
$manuNameEN = $dom->createElement(\'manuNameEN\',$manuNameEN);
$manuFolder = $dom->createElement(\'manuFolder\',$manuFolder);

$manual->appendChild($manuName);
$manual->appendChild($manuNameEN);
$manual->appendChild($manuFolder);

$manuals->appendChild($manual);
$dom->appendChild($manuals);
echo $dom->save($xmlpath);
}
else {
$dom->load($xmlpath);
$manuals = $dom->getElementsByTagName(\'manuals\');//获取manuals节点
$manual = $dom->createElement(\'manual\');//创建manual元素节点

$manuName = $dom->createElement(\'manuName\',$manuName);
$manuNameEN = $dom->createElement(\'manuNameEN\',$manuNameEN);
$manuFolder = $dom->createElement(\'manuFolder\',$manuFolder);

$manual->appendChild($manuName);
$manual->appendChild($manuNameEN);
$manual->appendChild($manuFolder);

$manuals->item(0)->appendChild($manual);//在名字为manuals的元素节点中的第一个元素后插入
echo $dom->save($xmlpath);
}
生成的XML格式如下：
<?xml version="1.0" encoding="utf-8"?>
<manuals>
<manual>
<manuName>PHP</manuName>
<manuNameEN>PHP</manuNameEN>
<manuFolder>php/</manuFolder>
</manual>
<manual>
<manuName>ASP</manuName>
<manuNameEN>ASP</manuNameEN>
<manuFolder>asp/</manuFolder>
</manual>
<manual>
<manuName>JScript</manuName>
<manuNameEN>JScript</manuNameEN>
<manuFolder>js/</manuFolder>
</manual>
</manuals>

需要说明的是，XML文档中不允许出现<>和&，请在插入数据之前预先处理好！