You can ignore the script if desired because it is an exact duplicate of the final test example contained in the xml parsing documentation on this site.  This script causes a browser message box to appear saying the page cannot be opened due to the server returning an invalid or unrecognized response.

<?php
$file = "xmltest.xml";

function trustedFile($file) {
    // only trust local files owned by ourselves
    if (!eregi("^([a-z]+)://", $file) 
        && fileowner($file) == getmyuid()) {
            return true;
    }
    return false;
}

function startElement($parser, $name, $attribs) {
    print "&lt;<font color=\"#0000cc\">$name</font>";
    if (sizeof($attribs)) {
        while (list($k, $v) = each($attribs)) {
            print " <font color=\"#009900\">$k</font>=\"<font 
                   color=\"#990000\">$v</font>\"";
        }
    }
    print "&gt;";
}

function endElement($parser, $name) {
    print "&lt;/<font color=\"#0000cc\">$name</font>&gt;";
}

function characterData($parser, $data) {
    print "<b>$data</b>";
}

function PIHandler($parser, $target, $data) {
    switch (strtolower($target)) {
        case "php":
            global $parser_file;
            // If the parsed document is "trusted", we say it is safe
            // to execute PHP code inside it.  If not, display the code
            // instead.
            if (trustedFile($parser_file[$parser])) {
                eval($data);
            } else {
                printf("Untrusted PHP code: <i>%s</i>", 
                        htmlspecialchars($data));
            }
            break;
    }
}

function defaultHandler($parser, $data) {
    if (substr($data, 0, 1) == "&" && substr($data, -1, 1) == ";") {
        printf('<font color="#aa00aa">%s</font>', 
                htmlspecialchars($data));
    } else {
        printf('<font size="-1">%s</font>', 
                htmlspecialchars($data));
    }
}

function externalEntityRefHandler($parser, $openEntityNames, $base, $systemId,
                                  $publicId) {
    if ($systemId) {
        if (!list($parser, $fp) = new_xml_parser($systemId)) {
            printf("Could not open entity %s at %s\n", $openEntityNames,
                   $systemId);
            return false;
        }
        while ($data = fread($fp, 4096)) {
            if (!xml_parse($parser, $data, feof($fp))) {
                printf("XML error: %s at line %d while parsing entity %s\n",
                       xml_error_string(xml_get_error_code($parser)),
                       xml_get_current_line_number($parser), $openEntityNames);
                xml_parser_free($parser);
                return false;
            }
        }
        xml_parser_free($parser);
        return true;
    }
    return false;
}


function new_xml_parser($file) {
    global $parser_file;

    $xml_parser = xml_parser_create();
    xml_parser_set_option($xml_parser, XML_OPTION_CASE_FOLDING, 1);
    xml_set_element_handler($xml_parser, "startElement", "endElement");
    xml_set_character_data_handler($xml_parser, "characterData");
    xml_set_processing_instruction_handler($xml_parser, "PIHandler");
    xml_set_default_handler($xml_parser, "defaultHandler");
    xml_set_external_entity_ref_handler($xml_parser, "externalEntityRefHandler");
    
    if (!($fp = @fopen($file, "r"))) {
        return false;
    }
    if (!is_array($parser_file)) {
        settype($parser_file, "array");
    }
    $parser_file[$xml_parser] = $file;
    return array($xml_parser, $fp);
}

if (!(list($xml_parser, $fp) = new_xml_parser($file))) {
    die("could not open XML input");
}

print "<pre>";
while ($data = fread($fp, 4096)) {
    if (!xml_parse($xml_parser, $data, feof($fp))) {
        die(sprintf("XML error: %s at line %d\n",
                    xml_error_string(xml_get_error_code($xml_parser)),
                    xml_get_current_line_number($xml_parser)));
    }
}
print "</pre>";
print "parse complete\n";
xml_parser_free($xml_parser);

echo phpinfo();
?>