PHP xml_set_external_entity_ref_handler() Function

<?php
// Create an XML parser
$parser=xml_parser_create();

function char($parser,$data) {
echo $data;
}

function ext_ent_handler($parser,$ent,$base,$sysID,$pubID)  {
echo "$ent<br>";
echo "$sysID<br>";
echo "$pubID<br>";
}

// Set the character data handler
xml_set_character_data_handler($parser,"char");

// Set the external entity reference handler
xml_set_external_entity_ref_handler($parser, "ext_ent_handler");

$fp=fopen("note_entity.xml","r");

while ($data=fread($fp,4096)) {
  // Parse XML data
  xml_parse($parser,$data,feof($fp)) or
  die (sprintf("XML Error: %s at line %d",
  xml_error_string(xml_get_error_code($parser)),
  xml_get_current_line_number($parser)));
}

xml_parser_free($parser);
fclose($fp);
?>