What potential pitfalls can arise when using <?=$TopNav?> in PHP code for navigation bars?

Using <?=$TopNav?> directly in PHP code can potentially lead to security vulnerabilities such as cross-site scripting (XSS) attacks if the $TopNav variable is not properly sanitized. To prevent this, it is recommended to use htmlspecialchars() function to escape any HTML characters in the variable before outputting it.

<?=htmlspecialchars($TopNav)?>