As of PHP 5.1, libxml options may be set using constants rather than the use of proprietary DomDocument properties.
DomDocument->resolveExternals is equivilant to setting
LIBXML_DTDLOAD
LIBXML_DTDATTR
DomDocument->validateOnParse is equivilant to setting
LIBXML_DTDLOAD
LIBXML_DTDVALID
PHP 5.1 users are encouraged to use the new constants.
Example:
DomDocument->load($file, LIBXML_DTDLOAD|LIBXML_DTDATTR);
DomDocument->load($file, LIBXML_DTDLOAD|LIBXML_DTDVALID);