Unserialize an XML document from a string or a file.
The way the document is unserialized is influenced by the options you set in the constructor or with setOptions().
string $data - either the file name of an XML document or a string containing the XML document.
boolean $isFile - indicates whether the first parameter should is a filename (TRUE) or an XML string (FALSE).
array $options - Options to override the options that have been set previously. The options will only be used for this unserialization and then reset the the options you set before.