What potential pitfalls should be avoided when working with form data in PHP, such as context switching with htmlspecialchars()?

When working with form data in PHP, a potential pitfall to avoid is context switching when using htmlspecialchars(). This can lead to double encoding of special characters, resulting in unexpected output or security vulnerabilities. To prevent this, always use htmlspecialchars() with the ENT_QUOTES flag to encode both double and single quotes properly.

// Avoid context switching with htmlspecialchars() by using the ENT_QUOTES flag
$unsafe_data = $_POST['input_data'];
$safe_data = htmlspecialchars($unsafe_data, ENT_QUOTES);