The DOMDocument class

(PHP 5, PHP 7)

简介

Represents an entire HTML or XML document; serves as the root of the document tree.

类摘要

DOMDocument extends DOMNode {
/* 属性 */
readonly public string $actualEncoding ;
readonly public DOMConfiguration $config ;
readonly public DOMDocumentType $doctype ;
readonly public DOMElement $documentElement ;
public string $documentURI ;
public string $encoding ;
public bool $formatOutput ;
readonly public DOMImplementation $implementation ;
public bool $preserveWhiteSpace = true ;
public bool $recover ;
public bool $resolveExternals ;
public bool $standalone ;
public bool $strictErrorChecking = true ;
public bool $substituteEntities ;
public bool $validateOnParse = false ;
public string $version ;
readonly public string $xmlEncoding ;
public bool $xmlStandalone ;
public string $xmlVersion ;
/* 方法 */
public __construct ([ string $version [, string $encoding ]] )
public DOMAttr createAttribute ( string $name )
public DOMAttr createAttributeNS ( string $namespaceURI , string $qualifiedName )
public DOMCDATASection createCDATASection ( string $data )
public DOMComment createComment ( string $data )
public DOMDocumentFragment createDocumentFragment ( void )
public DOMElement createElement ( string $name [, string $value ] )
public DOMElement createElementNS ( string $namespaceURI , string $qualifiedName [, string $value ] )
public DOMEntityReference createEntityReference ( string $name )
public DOMProcessingInstruction createProcessingInstruction ( string $target [, string $data ] )
public DOMText createTextNode ( string $content )
public DOMElement getElementById ( string $elementId )
public DOMNodeList getElementsByTagName ( string $name )
public DOMNodeList getElementsByTagNameNS ( string $namespaceURI , string $localName )
public DOMNode importNode ( DOMNode $importedNode [, bool $deep ] )
public mixed load ( string $filename [, int $options = 0 ] )
public bool loadHTML ( string $source [, int $options = 0 ] )
public bool loadHTMLFile ( string $filename [, int $options = 0 ] )
public mixed loadXML ( string $source [, int $options = 0 ] )
public void normalizeDocument ( void )
public bool registerNodeClass ( string $baseclass , string $extendedclass )
public bool relaxNGValidate ( string $filename )
public bool relaxNGValidateSource ( string $source )
public int save ( string $filename [, int $options ] )
public string saveHTML ([ DOMNode $node = NULL ] )
public int saveHTMLFile ( string $filename )
public string saveXML ([ DOMNode $node [, int $options ]] )
public bool schemaValidate ( string $filename [, int $flags ] )
public bool schemaValidateSource ( string $source [, int $flags ] )
public bool validate ( void )
public int xinclude ([ int $options ] )
/* 继承的方法 */
public DOMNode DOMNode::appendChild ( DOMNode $newnode )
public string DOMNode::C14N ([ bool $exclusive [, bool $with_comments [, array $xpath [, array $ns_prefixes ]]]] )
public int DOMNode::C14NFile ( string $uri [, bool $exclusive [, bool $with_comments [, array $xpath [, array $ns_prefixes ]]]] )
public DOMNode DOMNode::cloneNode ([ bool $deep ] )
public int DOMNode::getLineNo ( void )
public string DOMNode::getNodePath ( void )
public bool DOMNode::hasAttributes ( void )
public bool DOMNode::hasChildNodes ( void )
public DOMNode DOMNode::insertBefore ( DOMNode $newnode [, DOMNode $refnode ] )
public bool DOMNode::isDefaultNamespace ( string $namespaceURI )
public bool DOMNode::isSameNode ( DOMNode $node )
public bool DOMNode::isSupported ( string $feature , string $version )
public string DOMNode::lookupNamespaceURI ( string $prefix )
public string DOMNode::lookupPrefix ( string $namespaceURI )
public void DOMNode::normalize ( void )
public DOMNode DOMNode::removeChild ( DOMNode $oldnode )
public DOMNode DOMNode::replaceChild ( DOMNode $newnode , DOMNode $oldnode )
}

属性

actualEncoding

Deprecated. Actual encoding of the document, is a readonly equivalent to encoding.

config

Deprecated. Configuration used when DOMDocument::normalizeDocument() is invoked.

doctype

The Document Type Declaration associated with this document.

documentElement

This is a convenience attribute that allows direct access to the child node that is the document element of the document.

documentURI

The location of the document or NULL if undefined.

encoding

Encoding of the document, as specified by the XML declaration. This attribute is not present in the final DOM Level 3 specification, but is the only way of manipulating XML document encoding in this implementation.

formatOutput

Nicely formats output with indentation and extra space.

implementation

The DOMImplementation object that handles this document.

preserveWhiteSpace

Do not remove redundant white space. Default to TRUE.

recover

Proprietary. Enables recovery mode, i.e. trying to parse non-well formed documents. This attribute is not part of the DOM specification and is specific to libxml.

resolveExternals

Set it to TRUE to load external entities from a doctype declaration. This is useful for including character entities in your XML document.

standalone

Deprecated. Whether or not the document is standalone, as specified by the XML declaration, corresponds to xmlStandalone.

strictErrorChecking

Throws DOMException on errors. Default to TRUE.

substituteEntities

Proprietary. Whether or not to substitute entities. This attribute is not part of the DOM specification and is specific to libxml.

validateOnParse

Loads and validates against the DTD. Default to FALSE.

version

Deprecated. Version of XML, corresponds to xmlVersion.

xmlEncoding

An attribute specifying, as part of the XML declaration, the encoding of this document. This is NULL when unspecified or when it is not known, such as when the Document was created in memory.

xmlStandalone

An attribute specifying, as part of the XML declaration, whether this document is standalone. This is FALSE when unspecified.

xmlVersion

An attribute specifying, as part of the XML declaration, the version number of this document. If there is no declaration and if this document supports the "XML" feature, the value is "1.0".

注释

Note:

The DOM extension uses UTF-8 encoding. Use utf8_encode() and utf8_decode() to work with texts in ISO-8859-1 encoding or Iconv for other encodings.

参见

Table of Contents

User Contributed Notes

biker dot mike at gmx dot com 22-Aug-2016 10:36
Look out for the following gotcha when loading XML from a string:

<?php
$doc = new \DOMDocument;
$doc->documentURI = $myXmlFilename;
$doc->loadXML($myXmlString);
?>

documentURI is now set to the value of $myXmlFilename, right?

Wrong!

It's set to the current working directory.  If you want to manually set documentURI to something other than the CWD, do so AFTER the call to loadXML().

E.g.:
<?php
$doc = new \DOMDocument;
$doc->loadXML($myXmlString);
$doc->documentURI = $myXmlFilename;
?>

documentURI really is now set to the value of $myXmlFilename.
developer at nabtron dot com 17-Dec-2015 04:34
For those landing here and checking for encoding issue with utf-8 characteres, it's pretty easy to correct it, without adding any additional output tag to your html.

We'll be utilizing: mb_convert_encoding

Thanks to the user who shared: SmartDOMDocument in previous comments, I got the idea of solving it. However I truly wish that he shared the method instead of giving a link.

Anyway coming back to the solution, you can simply use:

<?php

            // checks if the content we're receiving isn't empty, to avoid the warning
            if ( empty( $content ) ) {
                return false;
            }

            // converts all special characters to utf-8
            $content = mb_convert_encoding($content, 'HTML-ENTITIES', 'UTF-8');

            // creating new document
            $doc = new DOMDocument('1.0', 'utf-8');

            //turning off some errors
            libxml_use_internal_errors(true);

            // it loads the content without adding enclosing html/body tags and also the doctype declaration
            $doc->LoadHTML($content, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);

            // do whatever you want to do with this code now

?>

I hope it solves the issue for someone! If you need my help or service to fix your code, you can reach me on nabtron.com or contact me at the email mentioned with this comment.
ingjetel at gmail dot com 14-May-2015 08:54
Easy function for basic output of XML file via DOM parsing

<?php
$dom = new DomDocument();
$dom->load("./file.xml") or die("error");
$start = $dom->documentElement;
fc($start);

function fc($node) {
  $child = $node->childNodes;
  foreach($child as $item) {
    if ($item->nodeType == XML_TEXT_NODE) {
      if (strlen(trim($item->nodeValue))) echo trim($item->nodeValue)."<br/>";
    }
    else if ($item->nodeType == XML_ELEMENT_NODE) fc($item);
  }
}
?>
qrworld.net 12-Nov-2014 01:35
In this post http://softontherocks.blogspot.com/2014/11/descargar-el-contenido-de-una-url_11.html I found a simple way to get the content of a URL with DOMDocument, loadHTMLFile and saveHTML().

function getURLContent($url){
    $doc = new DOMDocument;
    $doc->preserveWhiteSpace = FALSE;
    @$doc->loadHTMLFile($url);
    return $doc->saveHTML();
}
danny dot nunez15 at gmail dot com 28-Oct-2013 11:54
A simple function to grab all links in a page.

    function get_links($url) {

        // Create a new DOM Document to hold our webpage structure
        $xml = new DOMDocument();

        // Load the url's contents into the DOM

        $xml->loadHTMLFile($url);

        // Empty array to hold all links to return
        $links = array();

        //Loop through each <a> tag in the dom and add it to the link array
        foreach ($xml->getElementsByTagName('a') as $link) {
            $url = $link->getAttribute('href');
            if (!empty($url)) {
                $links[] = $link->getAttribute('href');
            }
        }

        //Return the links
        return $links;
    }
sites.sitesbr.net 22-Jan-2013 09:37
How to objetify a DomDocument with hierarchy like:
<root>
    <item>
          <prop1>info1</prop1>
          <prop2>info2</prop2>
          <prop3>info3</prop3>
     </item>
    <item>
          <prop1>info1</prop1>
          <prop2>info2</prop2>
          <prop3>info3</prop3>
     </item>
</root>

It's possible to use in object style to retrieve information, as:

<?php
     $theNodeValue = $aitem->prop1;
?>

Here is the code: one Class and 2 functions.

<?php
 class ArrayNode{
       public $nodeName, $nodeValue;
 }

 function getChildNodeElements( $domNode ){
     $nodes = array();
     for( $i=0; $i < $domNode->childNodes->length; $i++){
       $cn = $domNode->childNodes->item($i);
       if( $cn->nodeType == 1){
           $nodes[] = $cn;
           }
     }
    return $nodes;
 }

 function getArrayNodes( $domDoc ){
     $res = array();

       for( $i=0; $i < $domDoc->childNodes->length; $i++){
       $cn = $domDoc->childNodes->item($i);
       # The first is the root tag...
          if( $cn->nodeType == 1){
               # But we want it's childNodes.
                $sub_cn = getChildNodeElements( $cn);
                # Found the tagName:
                $baseItemTagName = $sub_cn[0]->nodeName;
                break;
            }
        }

       $dnl = $domDoc->getElementsByTagName( $baseItemTagName);

       for( $i=0; $i< $dnl->length; $i++){
          $arrayNode = new ArrayNode();

      # Summary
      $arrayNode->nodeName = $dnl->item($i)->nodeName;
      $arrayNode->nodeValue = $dnl->item($i)->nodeValue;

      # Child Nodes
      $cn = $dnl->item($i)->childNodes;
      for( $k=0; $k<$cn->length; $k++){
           if( $cn->item($k)->nodeName == "#text" && trim($cn->item($k)->nodeValue) == "") continue;
           $arrayNode->{$cn->item($k)->nodeName} = $cn->item($k)->nodeValue;
      }

      # Attributes
      $attr = $dnl->item($i)->attributes;
      for( $k=0; $k < $attr->length; $k++){
           if(! is_null($attr)){
            if( $attr->item($k)->nodeName == "#text" && trim($attr->item($k)->nodeValue) == "") continue;
            $arrayNode->{$attr->item($k)->nodeName} = $attr->item($k)->nodeValue;
           }
      }

      $res[] = $arrayNode;

       }

     return $res;
 }
?>

To use it:

<?php

  # First you load a XML in a DomDocument variable.

   $url = "/path/to/yourxmlfile.xml";
   $domSrc = file_get_contents($url);
   $dom = new DomDocument();
   $dom->loadXML( $domSrc );

  # Then, you get the ArrayNodes from the DomDocument.

    $ans = getArrayNodes( $dom );

 
    for( $i=0; $i < count( $ans ) ; $i++){

    $cn =  $ans[ $i];

    $info1 =  $cn->prop1;
    $info2 =  $cn->prop2;
    $info3 =  $cn->prop3;
     
         // ...
 
   }

?>
Nick M 01-Jun-2011 07:16
You may need to save all or part of a DOMDocument as an XHTML-friendly string, something compliant with both XML and HTML 4. Here's the DOMDocument class extended with a saveXHTML method:

<?php

/**
 * XHTML Document
 *
 * Represents an entire XHTML DOM document; serves as the root of the document tree.
 */
class XHTMLDocument extends DOMDocument {

  /**
   * These tags must always self-terminate. Anything else must never self-terminate.
   *
   * @var array
   */
  public $selfTerminate = array(
      'area','base','basefont','br','col','frame','hr','img','input','link','meta','param'
  );
 
  /**
   * saveXHTML
   *
   * Dumps the internal XML tree back into an XHTML-friendly string.
   *
   * @param DOMNode $node
   *         Use this parameter to output only a specific node rather than the entire document.
   */
  public function saveXHTML(DOMNode $node=null) {
   
    if (!$node) $node = $this->firstChild;
   
    $doc = new DOMDocument('1.0');
    $clone = $doc->importNode($node->cloneNode(false), true);
    $term = in_array(strtolower($clone->nodeName), $this->selfTerminate);
    $inner='';
   
    if (!$term) {
      $clone->appendChild(new DOMText(''));
      if ($node->childNodes) foreach ($node->childNodes as $child) {
        $inner .= $this->saveXHTML($child);
      }
    }
   
    $doc->appendChild($clone);
    $out = $doc->saveXML($clone);
   
    return $term ? substr($out, 0, -2) . ' />' : str_replace('><', ">$inner<", $out);

  }

}

?>

This hasn't been benchmarked, but is probably significantly slower than saveXML or saveHTML and should be used sparingly.
evert at er dot nl 20-Nov-2010 11:17
A nice and simple node 2 array I wrote, worth a try ;)

<?php
function getArray($node)
{
    $array = false;

    if ($node->hasAttributes())
    {
        foreach ($node->attributes as $attr)
        {
            $array[$attr->nodeName] = $attr->nodeValue;
        }
    }

    if ($node->hasChildNodes())
    {
        if ($node->childNodes->length == 1)
        {
            $array[$node->firstChild->nodeName] = $node->firstChild->nodeValue;
        }
        else
        {
            foreach ($node->childNodes as $childNode)
            {
                if ($childNode->nodeType != XML_TEXT_NODE)
                {
                    $array[$childNode->nodeName][] = $this->getArray($childNode);
                }
            }
        }
    }

    return $array;
}
?>
admin at beerpla dot net 12-Mar-2010 11:12
After seeing many complaints about certain DOMDocument shortcomings, such as bad handling of encodings and always saving HTML fragments with <html>, <head>, and DOCTYPE, I decided that a better solution is needed.

So here it is: SmartDOMDocument. You can find it at http://beerpla.net/projects/smartdomdocument/

Currently, the main highlights are:

- SmartDOMDocument inherits from DOMDocument, so it's very easy to use - just declare an object of type SmartDOMDocument instead of DOMDocument and enjoy the new behavior on top of all existing functionality (see example below).

- saveHTMLExact() - DOMDocument has an extremely badly designed "feature" where if the HTML code you are loading does not contain <html> and <body> tags, it adds them automatically (yup, there are no flags to turn this behavior off).
Thus, when you call $doc->saveHTML(), your newly saved content now has <html><body> and DOCTYPE in it. Not very handy when trying to work with code fragments (XML has a similar problem).
SmartDOMDocument contains a new function called saveHTMLExact() which does exactly what you would want - it saves HTML without adding that extra garbage that DOMDocument does.

- encoding fix - DOMDocument notoriously doesn't handle encoding (at least UTF-8) correctly and garbles the output.
SmartDOMDocument tries to work around this problem by enhancing loadHTML() to deal with encoding correctly. This behavior is transparent to you - just use loadHTML() as you would normally.

- SmartDOMDocument Object As String - you can use a SmartDOMDocument object as a string which will print out its contents.
For example:
<?php
echo "Here is the HTML: $smart_dom_doc";
?>

I'm going to maintain this code and try to fix bugs as they come in.

Enjoy.
tloach at gmail dot com 05-Feb-2010 07:01
For anyone else who has been having issues with formatOuput not working, here is a work-around:

rather than just doing something like:

<?php
$outXML = $xml->saveXML();
?>

force it to reload the XML from scratch, then it will format correctly:

<?php
$outXML = $xml->saveXML();
$xml = new DOMDocument();
$xml->preserveWhiteSpace = false;
$xml->formatOutput = true;
$xml->loadXML($outXML);
$outXML = $xml->saveXML();
?>
jay at jaygilford dot com 27-Jan-2010 05:46
Here's a small function I wrote to get all page links using the DOMDocument which will hopefully be of use to others

<?php
/**
 * @author Jay Gilford
 */
 
/**
 * get_links()
 *
 * @param string $url
 * @return array
 */
function get_links($url) {
 
    // Create a new DOM Document to hold our webpage structure
    $xml = new DOMDocument();
 
    // Load the url's contents into the DOM
    $xml->loadHTMLFile($url);
 
    // Empty array to hold all links to return
    $links = array();
 
    //Loop through each <a> tag in the dom and add it to the link array
    foreach($xml->getElementsByTagName('a') as $link) {
        $links[] = array('url' => $link->getAttribute('href'), 'text' => $link->nodeValue);
    }
 
    //Return the links
    return $links;
}
?>
fcartegnie 31-Oct-2009 10:30
Be careful with formatOutput().

Creating an empty node like this:
createElement('foo','')
instead of
createElement('foo')
will break formatOutput.
PhilipWayneRollins at gmail dot com 15-Aug-2009 10:32
If you want to use the DOMDocument to create xHTML documents here is a simple class

Note this is designed for creating xHTML documents from scratch but could be easily extended to work with xHTML documents. Also this is for xHTML not XML.

<?php
    class Document
    {
        public $doctype;
        public $head;
        public $title = 'Sensei Ninja';
        public $body;
        private $styles;
        private $metas;
        private $scripts;
        private $document;
       
       
        function __construct (  )
        {
            $this->document = new DOMDocument( );
            $this->head = $this->document->createElement( 'head', ' ' );
            $this->body = $this->document->createElement( 'body', ' ' );
        }
       
       
        public function addStyleSheet ( $url, $media='all' )
        {
            $element = $this->document->createElement( 'link' );
            $element->setAttribute( 'type', 'text/css' );
            $element->setAttribute( 'href', $url );
            $element->setAttribute( 'media', $media );
            $this->styles[] = $element;
        }
       
       
        public function addScript ( $url )
        {
            $element = $this->document->createElement( 'script', ' ' );
            $element->setAttribute( 'type', 'text/javascript' );
            $element->setAttribute( 'src', $url );
            $this->scripts[] = $element;
        }
       
       
        public function addMetaTag ( $name, $content )
        {
            $element = $this->document->createElement( 'meta' );
            $element->setAttribute( 'name', $name );
            $element->setAttribute( 'content', $content );
            $this->metas[] = $element;
        }
       
       
        public function setDescription ( $dec )
        {
            $this->addMetaTag( 'description', $dec );
        }
       
       
        public function setKeywords ( $keywords )
        {
            $this->addMetaTag( 'keywords', $keywords );
        }
       
        public function createElement ( $nodeName, $nodeValue=null )
        {
          return $this->document->createElement( $nodeName, $nodeValue );
        }
       
        public function assemble ( )
        {
            // Doctype creation
            $doctype = '<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML TRANSITIONAL 1.0//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">';
           
            // Create the head element
            $title = $this->document->createElement( 'title', $this->title );
            // Add stylesheets if needed
            if ( is_array( $this->styles ))
                foreach ( $this->styles as $element )
                    $this->head->appendChild( $element );
            // Add scripts if needed
            if(  is_array( $this->scripts ))
                foreach ( $this->scripts as $element )
                    $this->head->appendChild( $element );
            // Add meta tags if needed
            if ( is_array( $this->metas ))
                foreach ( $this->metas as $element )
                    $this->head->appendChild( $element );
            $this->head->appendChild( $title );
           
            // Create the document
            $html = $this->document->createElement( 'html' );
            $html->setAttribute( 'xmlns', 'http://www.w3.org/1999/xhtml' );
            $html->setAttribute( 'xml:lang', 'en' );
            $html->setAttribute( 'lang', 'en' );
            $html->appendChild( $this->head );
            $html->appendChild( $this->body );
           
           
            $this->document->appendChild( $html );
            return $doctype . $this->document->saveXML( );
        }
       
    }
   
?>

Small example

<?php
        $document = new Document( );
    $document->title = 'Hello';
    $document->addStyleSheet( 'StyleSheets/main.css' );
    $div = $document->createElement( 'div' );
    $div->nodeValue = 'Hello, world!';
    $div->setAttribute( 'style', 'color: red;' );
    $document->body->appendChild( $div );
    printf( '%s', $document->assemble( ) );
?>
cmyk777 at gmail dot com 23-May-2009 09:31
This function may help to debug current dom element:

<?php
function dom_dump($obj) {
    if ($classname = get_class($obj)) {
        $retval = "Instance of $classname, node list: \n";
        switch (true) {
            case ($obj instanceof DOMDocument):
                $retval .= "XPath: {$obj->getNodePath()}\n".$obj->saveXML($obj);
                break;
            case ($obj instanceof DOMElement):
                $retval .= "XPath: {$obj->getNodePath()}\n".$obj->ownerDocument->saveXML($obj);
                break;
            case ($obj instanceof DOMAttr):
                $retval .= "XPath: {$obj->getNodePath()}\n".$obj->ownerDocument->saveXML($obj);
                //$retval .= $obj->ownerDocument->saveXML($obj);
                break;
            case ($obj instanceof DOMNodeList):
                for ($i = 0; $i < $obj->length; $i++) {
                    $retval .= "Item #$i, XPath: {$obj->item($i)->getNodePath()}\n".
"{$obj->item($i)->ownerDocument->saveXML($obj->item($i))}\n";
                }
                break;
            default:
                return "Instance of unknown class";
        }
    } else {
        return 'no elements...';
    }
    return htmlspecialchars($retval);
}
?>

Example usage:

<?php
$dom = new DomDocument();
$dom->load('test.xml');
$body = $dom->documentElement->getElementsByTagName('book');
echo '<pre>'.dom_dump($body).'<pre>';
?>

Output:

Instance of DOMNodeList, node list:
Item #0, XPath: /library/book[1]
<book isbn="0345342968">
<title>Fahrenheit 451</title>
<author>R. Bradbury</author>
<publisher>Del Rey</publisher>
</book>
Item #1, XPath: /library/book[2]
<book isbn="0048231398">
<title>The Silmarillion</title>
<author>J.R.R. Tolkien</author>
<publisher>G. Allen &amp; Unwin</publisher>
</book>
Item #2, XPath: /library/book[3]
<book isbn="0451524934">
<title>1984</title>
<author>G. Orwell</author>
<publisher>Signet</publisher>
</book>
Item #3, XPath: /library/book[4]
<book isbn="031219126X">
<title>Frankenstein</title>
<author>M. Shelley</author>
<publisher>Bedford</publisher>
</book>
Item #4, XPath: /library/book[5]
<book isbn="0312863551">
<title>The Moon Is a Harsh Mistress</title>
<author>R. A. Heinlein</author>
<publisher>Orb</publisher>
</book>
Fernando H 11-Apr-2008 09:48
Showing a quick example of how to use this class, just so that new users can get a quick start without having to figure it all out by themself. ( At the day of posting, this documentation just got added and is lacking examples. )

<?php

// Set the content type to be XML, so that the browser will   recognise it as XML.
header( "content-type: application/xml; charset=ISO-8859-15" );

// "Create" the document.
$xml = new DOMDocument( "1.0", "ISO-8859-15" );

// Create some elements.
$xml_album = $xml->createElement( "Album" );
$xml_track = $xml->createElement( "Track", "The ninth symphony" );

// Set the attributes.
$xml_track->setAttribute( "length", "0:01:15" );
$xml_track->setAttribute( "bitrate", "64kb/s" );
$xml_track->setAttribute( "channels", "2" );

// Create another element, just to show you can add any (realistic to computer) number of sublevels.
$xml_note = $xml->createElement( "Note", "The last symphony composed by Ludwig van Beethoven." );

// Append the whole bunch.
$xml_track->appendChild( $xml_note );
$xml_album->appendChild( $xml_track );

// Repeat the above with some different values..
$xml_track = $xml->createElement( "Track", "Highway Blues" );

$xml_track->setAttribute( "length", "0:01:33" );
$xml_track->setAttribute( "bitrate", "64kb/s" );
$xml_track->setAttribute( "channels", "2" );
$xml_album->appendChild( $xml_track );

$xml->appendChild( $xml_album );

// Parse the XML.
print $xml->saveXML();

?>

Output:
<Album>
  <Track length="0:01:15" bitrate="64kb/s" channels="2">
    The ninth symphony
    <Note>
      The last symphony composed by Ludwig van Beethoven.
    </Note>
  </Track>
  <Track length="0:01:33" bitrate="64kb/s" channels="2">Highway Blues</Track>
</Album>

If you want your PHP->DOM code to run under the .xml extension, you should set your webserver up to run the .xml extension with PHP ( Refer to the installation/configuration configuration for PHP on how to do this ).

Note that this:
<?php
$xml = new DOMDocument( "1.0", "ISO-8859-15" );
$xml_album = $xml->createElement( "Album" );
$xml_track = $xml->createElement( "Track" );
$xml_album->appendChild( $xml_track );
$xml->appendChild( $xml_album );
?>

is NOT the same as this:
<?php
// Will NOT work.
$xml = new DOMDocument( "1.0", "ISO-8859-15" );
$xml_album = new DOMElement( "Album" );
$xml_track = new DOMElement( "Track" );
$xml_album->appendChild( $xml_track );
$xml->appendChild( $xml_album );
?>

although this will work:
<?php
$xml = new DOMDocument( "1.0", "ISO-8859-15" );
$xml_album = new DOMElement( "Album" );
$xml->appendChild( $xml_album );
?>