multiple-error-handlers.php

<?php

function append_error_handler($handler) {
    set_error_handlers(array(set_error_handler($handler), $handler));
}

function prepend_error_handler($handler) {
    set_error_handlers(array($handler, set_error_handler($handler)));
}

function set_error_handlers($handlers) {
    $handlers = (is_array($handlers) ? $handlers : array($handlers));
    set_error_handler(function ($level, $message, $file = null, $line = null, $context = null) use ($handlers) {
        foreach ($handlers as $handler) {
            if ($handler) {
                call_user_func($handler, $level, $message, $file, $line, $context);
            }
        }
    });
}