// Load the XML document $xmlDoc = new DOMDocument(); $xmlDoc->load('myXMLFile.xml'); // Load the RelaxNG schema $rngDoc = new DOMDocument(); $rngDoc->load('myRNGSchema.rng'); // Validate the XML document against the RelaxNG schema if ($xmlDoc->relaxNGValidate($rngDoc)) { echo "XML document is valid against the RelaxNG schema."; } else { echo "XML document is not valid against the RelaxNG schema."; }In this example, the XML document and the RelaxNG schema are loaded into separate DOM documents, and the `relaxNGValidate` method is used to check if the XML document is valid against the schema. If the XML document is valid, the code will output "XML document is valid against the RelaxNG schema."; otherwise, it will output "XML document is not valid against the RelaxNG schema.". As mentioned earlier, the PHP DOMDocument relaxNGValidate is a built-in feature in the PHP language, so no library or package is needed.