ler xml e escrever

<?php

$name = $_POST['pesquisa_nome'];
$nomee = $_POST['pesquisa_usuario'];
$emaill = $_POST['pesquisa_email'];
$senhaa = $_POST['rpassword'];

$DOMDocument = new DOMDocument( '1.0', 'utf-8' );
      $DOMDocument->preserveWhiteSpace = false;
      $DOMDocument->load( 'usuarios.xml' );
      $DOMXPath = new DOMXPath( $DOMDocument );
      if( $DOMXPath->query( './/usuario[email="$emaill"]' )->length >= 1 ){
          echo 'Usuário já cadastrado';
          exit();
      }

      else{
      $DOMDocument = new DOMDocument( '1.0', 'utf-8' );
      $DOMDocument->preserveWhiteSpace = false;
      $DODMocument->formatOutput = true;
      $DOMDocument->load( 'usuarios.xml' );
      $Usuarios = $DOMDocument->getElementsByTagName( 'usuarios' )->item( 0 );


      $Dados = Array(
             'nome' => $name,
             'sobrenome' => '',
             'email' => $emaill,
             'login' => $nomee,
             'senha' => $senhaa,
             'ip' => $_SERVER[ 'REMOTE_ADDR' ]
      );
      $Usuario = $Usuarios->appendChild( $DOMDocument->createElement( 'usuario' ) );
      foreach( $Dados as $index => $data ){
            $Element = $Usuario->appendChild( $DOMDocument->createElement( $index ) );
            $Element->appendChild( $DOMDocument->createCDATASection( $data ) );
      }
      $DODMocument->formatOutput = true;
      $DOMDocument->preserveWhiteSpace = false;
      $DOMDocument->save( 'usuarios.xml' );
      }
      ?>