What are the potential pitfalls of using PHP5-specific features in a PHP script that needs to be compatible with PHP4?

Using PHP5-specific features in a script that needs to be compatible with PHP4 can cause compatibility issues and errors for users still running PHP4. To ensure compatibility, it's best to avoid using PHP5-specific features and instead stick to more universally supported functions and syntax.

// Example of using PHP5-specific features (namespaces) that may cause issues in PHP4
namespace MyNamespace;

// To ensure compatibility with PHP4, avoid using namespaces and stick to traditional global scope