What is the correct structure for XML documents when using simplexml_load_file in PHP?

When using simplexml_load_file in PHP to load and parse an XML document, it is important to ensure that the XML document has a correct structure. This includes having a single root element that encloses all other elements, properly nested elements, and well-formed tags. If the XML document does not have a correct structure, simplexml_load_file may throw an error or fail to parse the document correctly.

$xml = simplexml_load_file('example.xml');
if($xml) {
    // XML document has been successfully loaded and parsed
    // Perform operations on the XML data here
} else {
    // Error loading or parsing the XML document
    echo "Error loading XML file";
}