ob_list_handlers in PHP

ob_list_handlers — List all output handlers in use
Syntax: array ob_list_handlers ( void )
Lists all output handlers in use.
Return Values:This will return an array with the output handlers in use (if any). If output_buffering is enabled or an anonymous function was used with ob_start(), ob_list_handlers() will return "default output handler".
Example #1

<?php
//using output_buffering=On
print_r(ob_list_handlers());
ob_end_flush();

ob_start("ob_gzhandler");
print_r(ob_list_handlers());
ob_end_flush();

// anonymous functions
ob_start(function($string) { return $string; });
print_r(ob_list_handlers());
ob_end_flush();
?>
Output:

Array
(
    [0] => default output handler
)

Array
(
    [0] => ob_gzhandler
)

Array
(
    [0] => Closure::__invoke
)