How can one effectively handle form data and variables in PHP, especially when dealing with XML or complex data structures?

When handling form data and variables in PHP, especially when dealing with XML or complex data structures, it is important to sanitize and validate the input to prevent security vulnerabilities. One effective way to handle form data and variables in PHP is to use functions like htmlspecialchars() to prevent XSS attacks and filter_input() to sanitize input. Additionally, when working with XML or complex data structures, it is recommended to use libraries like SimpleXML or DOMDocument to parse and manipulate the data securely.

// Example of handling form data and variables securely in PHP
$input_data = $_POST['input_data']; // Assuming input data is coming from a form submission

// Sanitize input data to prevent XSS attacks
$sanitized_data = htmlspecialchars($input_data);

// Validate input data using filter_input
$filtered_data = filter_input(INPUT_POST, 'input_data', FILTER_SANITIZE_STRING);

// Example of parsing XML data using SimpleXML
$xml_data = simplexml_load_string($input_data);
foreach ($xml_data->children() as $child) {
    // Process XML data as needed
}