fns.php

<?php

// cascading configurations via
// merging with defaults options

$defaults = array(
    'foo'  => 'bar',
    'baz'  => 'qux',
    'quux' => 'fred',
);

$option1 = array(
    'foo' => 'abc',
    'abc' => 'def',
);

$option2 = array(
    'baz' => 'xyz',
    'abc' => '123',
);

$options = array_merge($defaults, $option1, $option2);

print_r($options);

/*
Array
(
    [foo] => abc
    [baz] => xyz
    [quux] => fred
    [abc] => 123
)
*/