What is the array_udiff_uassoc means in these codes

<?php

function user_key_compare_func($k1, $k2) {

    echo sprintf("debug key: %s vs %s %s\n", $k1, $k2, $k1===$k2 ? 0 : ($k1>$k2?1:-1) ); //debug行

    if ( $k1 === $k2 ) {

        return 0;

    }

    return $k1 > $k2 ? 1 : -1;

}

function user_value_compare_func($v1, $v2) {

    echo sprintf("debug value: %s vs %s %s\n", $v1, $v2, $v1===$v2 ? 0 : ($v1>$v2?1:-1) ); //debug行

    if ( $v1 === $v2 ) {

        return 0;

    }

    return $v1 > $v2 ? 1 : -1;

}

$arr1 = array('usage', 'name'=>'aiezu', 'suffix'=>'com',);

$arr2 = array('0'=>'usage', 'name'=>'coolit');

print_r(array_udiff_uassoc($arr1, $arr2, 'user_value_compare_func', 'user_key_compare_func'));