How can PHP developers ensure that input values are properly sanitized before displaying them in HTML?

PHP developers can ensure that input values are properly sanitized before displaying them in HTML by using functions like htmlspecialchars() or htmlentities() to encode special characters in the input values. This helps prevent XSS (Cross-Site Scripting) attacks by converting characters like <, >, ", ', and & into their respective HTML entities. By sanitizing input values before displaying them in HTML, developers can protect their websites from malicious scripts being injected into the page.

// Example of sanitizing input values before displaying them in HTML
$user_input = "<script>alert('XSS attack!');</script>";
$sanitized_input = htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');
echo $sanitized_input;