(PHP 5 >= 5.3.0, PHP 7)
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;
}
?>