How can PHP developers ensure that their links are clean and valid HTML code?

PHP developers can ensure that their links are clean and valid HTML code by using the `htmlspecialchars` function to escape special characters in the link URL. This will prevent any potential security vulnerabilities and ensure that the link is properly formatted in the HTML code.

$url = "https://www.example.com/page.php?param=<script>alert('xss');</script>";
$clean_url = htmlspecialchars($url, ENT_QUOTES, 'UTF-8');
echo '<a href="' . $clean_url . '">Click here</a>';