Working With Output Handlers

When invoked, output handlers are passed the contents of the buffer and a bitmask indicating the status of output buffering.

handler ( string $buffer , int $phase = ?): string

buffer: Contents of the output buffer.
phase: Bitmask of PHP_OUTPUT_HANDLER_* constants .

Warning

Calling any of the following functions from within an output handler will result in a fatal error: ob_clean(), ob_end_clean(), ob_end_flush(), ob_flush(), ob_get_clean(), ob_get_flush(), ob_start().

Note: If the PHP_OUTPUT_HANDLER_DISABLED of a handler is set, the handler will not be invoked by calling ob_end_clean(), ob_end_flush(), ob_get_clean(), ob_get_flush() or during PHP's shutdown process. This flag has no effect on when calling ob_clean() or ob_flush().

Note: The working directory of the script can change inside the shutdown function under some web servers, e.g. Apache or the built-in web server.