Included files will default to the global namespace.
<?php
//test.php
namespace test {
  include 'test1.inc';
  echo '-',__NAMESPACE__,'-<br />';
}
?>

<?php
//test1.inc
  echo '-',__NAMESPACE__,'-<br />';
?>

Results of test.php:

--
-test-

Note that variables aren't part of the namespace so they are always global (or scoped to function, etc.) and can't be accessed the same way as other namespace stuff.So no:    namespace Foo;    $var = "hello";    echo \Foo\$var;

In namespaced context the Exception class needs to be prefixed with global prefix operator.<?phpnamespace hey\ho\lets\go;class MyClass{    public function failToCatch()    {        try {            $thing = somethingThrowingAnException();        } catch (Exception $ex) {              // Not catched        }    }    public function succeedToCatch()    {        try {            $thing = somethingThrowingAnException();        } catch (\Exception $ex) {              // This is now catched        }    }}

To define an associative array (hash) so that it is part of the namespace, instead of going into the global namespace, just declare it as const, istead of as a variable.This is handy for lookup tables, config settings, etc.// Example.  Instead of writing:$my_datatypes = [    "sterility" =>  [      "xlsx" => [        "Sample Type",        "Run Pass/Fail",        "Result"       ],      "db" => [        "SampleType",        "RunPassFail",        "Result"       ]    ]];// ...declare the lookup table like this:const MY_DATATYPES = [    "sterility" =>  [      "xlsx" => [        "Sample Type",        "Run Pass/Fail",        "Result"       ],      "db" => [        "SampleType",        "RunPassFail",        "Result"       ]    ]];// ...and it will be declared within the current namespace.