PHP Basics -> Namespaces

While Preparing for Examination, you must be able to reply following questions.

1. What is namespaces in PHP?
2. What is difference between namespace operator (namespace) and namespace constant(__NAMESPACE__).
3. What are the significance of namespaces?
4. Which version of PHP support namespaces?
5. How to use a function that belongs to some namespaces.

If you have any doubt then let me know?