How can PHP developers ensure the safe handling of HTML code input from users in their applications?

PHP developers can ensure the safe handling of HTML code input from users by using the htmlspecialchars function to escape special characters in the input. This function converts characters like < and > into their HTML entity equivalents, preventing any potential malicious code injection. By sanitizing user input in this way, developers can protect their applications from cross-site scripting (XSS) attacks.

$user_input = "<script>alert('XSS attack!');</script>";
$safe_input = htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');
echo $safe_input;