XMLReader::setRelaxNGSchema

Make sure to load your data prior to calling ->setRelaxNGSchema() otherwise you will get an error.

<?php
$xml_reader = new XMLReader();
$xml_reader->setRelaxNGSchema($rng_schema);
$xml_reader->xml($xml_data);
?>
Above code generates the following warning: "Warning: XMLReader::setRelaxNGSchemaSource()
[xmlreader.setrelaxngschemasource]: Unable to set schema. This must be
set prior to reading or schema contains errors."

whereas the following does not generate a warning:
<?php
$xml_reader = new XMLReader();
$xml_reader->xml($xml_data); // or $xml_reader->xml($xml_file);
$xml_reader->setRelaxNGSchema($rng_schema);
?>

cf. http://bugs.php.net/bug.php?id=46978