Using namespaces: Aliasing/Importing
Using namespaces: fallback to global function/constant
Namespaces
PHP Manual

## Global space

Without any namespace definition, all class and function definitions are placed into the global space - as it was in PHP before namespaces were supported. Prefixing a name with \ will specify that the name is required from the global space even in the context of the namespace.

Example #1 Using global space specification

`<?php
namespace A\B\C;
/* This function is A\B\C\fopen */
function fopen() {
/* ... */
$f = \fopen(...); // call global fopen
return $f;
}
?>`