This function will send the contents of the output
buffer (if any). If you want to further process the buffer's
contents you have to call
ob_get_contents() before
ob_flush() as the buffer contents are discarded after ob_flush() is called.
This function does not destroy the output buffer like
ob_end_flush() does.
See also ob_get_contents(),
ob_clean(), ob_end_flush() and
ob_end_clean().