An aspect that is critical to advanced PHP development is the use of namespaces. The arbitrarily defined namespace becomes a prefix to the class name, thereby avoiding the problem of accidental class duplication, and allowing you extraordinary freedom of development. Another benefit to the use of a namespace, assuming it matches the directory structure, is that it facilitates autoloading, as discussed in Chapter 1, Building a Foundation.
namespaceat the top of the code file:
As with the recommendation to have only one class per file, likewise you should have only one namespace per file.