What is the difference between array_udiff_assoc() and array_diff_uassoc()?

What is the difference between array_udiff_assoc() and array_diff_uassoc()?

For array_udiff_assoc(), I have this code:

function myfunction($v1,$v2)
{
    if ($v1===$v2) {
        return 0;
    }
    return 1;
}
 
$a1 = ["a" => "Cat", "b" => "Dog", "c" => "Horse"];
$a2 = ["a" => "Cat", "b" => "Horse", "c" => "Dog"];
print_r(array_udiff_assoc($a1, $a2, "myfunction"));

result

Array ( [b] Dog [c] => Horse )

also array_diff_uassoc():

function myfunction($v1,$v2)
{
    if ($v1===$v2) {
        return 0;
    }
    return 1;
}
     
$a1 = ["a" => "Cat", "b" => "Dog", ​"c" => "Horse"];
​$a2 = ["a" => "Cat", "b" => "Horse", "c" => "Dog"];
​print_r(array_diff_uassoc($a1, $a2, "myfunction"));

The result is same as first one:

Array ( [b] Dog [c] => Horse )

If they have any difference, what is it? The PHP manual does not says that they are aliases of each other.

Perhaps a battery of test cases will clear up any confusion between these related native functions. I'll consistently use the native case-insensitive comparison function strcasecmp() to simplify the demonstration/explanation.

Here is the plain English explanation of how each function will behave:

1. array_diff() - case-sensitive value-only comparisons
2. array_diff_key() - case-sensitive key-only comparisons
3. array_diff_ukey() - case-insensitive key-only comparisons
4. array_diff_assoc() - case-sensitive key and case-sensitive value comparisons
5. array_diff_uassoc() - * first-occurring case-insensitive key and case-sensitive value comparisons
6. array_udiff() - case-insensitive value-only comparisons
7. array_udiff_assoc() - case-sensitive key and case-insensitive value comparisons
8. array_udiff_uassoc() - case-insensitive key and case-insensitive value comparisons

*Pay very close attention to how 5. array_diff_uassoc() behaves differently with respect to the ['c' => 'd'] and ['m' => 'n'] comparisons due to the order of qualifying occurences in the $second array.

Code: (Demo)

$first = [
    'A' => 'B',
    'c' => 'd',
    'E' => 'f',
    'g' => 'I',
    'k' => 'F',
    'm' => 'n',
    'o' => 'p',
];

$second = [
    'a' => 'b',
    'A' => 'b',
    'C' => 'd',
    'c' => 'D',
    'e' => 'F',
    'G' => 'H',
    'i' => 'B',
    'J' => 'D',
    'm' => 'N',
    'M' => 'n',
    'O' => 'r',
];

echo "array_diff()\n";
var_export(array_diff($first, $second));
echo "\n---\narray_diff_key()\n";
var_export(array_diff_key($first, $second));
echo "\n---\narray_diff_ukey()\n";
var_export(array_diff_ukey($first, $second, 'strcasecmp'));
echo "\n---\narray_diff_assoc()\n";
var_export(array_diff_assoc($first, $second));
echo "\n---\narray_diff_uassoc()\n";
var_export(array_diff_uassoc($first, $second, 'strcasecmp'));
echo "\n---\narray_udiff()\n";
var_export(array_udiff($first, $second, 'strcasecmp'));
echo "\n---\narray_udiff_assoc()\n";
var_export(array_udiff_assoc($first, $second, 'strcasecmp'));
echo "\n---\narray_udiff_uassoc()\n";
var_export(array_udiff_uassoc($first, $second, 'strcasecmp', 'strcasecmp'));

Output:

array_diff()
array (
  'E' => 'f',
  'G' => 'I',
  'o' => 'p',
)
---
array_diff_key()
array (
  'E' => 'f',
  'k' => 'F',
  'o' => 'p',
)
---
array_diff_ukey()
array (
  'k' => 'F',
)
---
array_diff_assoc()
array (
  'A' => 'B',
  'c' => 'd',
  'E' => 'f',
  'G' => 'I',
  'k' => 'F',
  'm' => 'n',
  'o' => 'p',
)
---
array_diff_uassoc()
array (
  'A' => 'B',
  'E' => 'f',
  'G' => 'I',
  'k' => 'F',
  'm' => 'n',
  'o' => 'p',
)
---
array_udiff()
array (
  'G' => 'I',
  'o' => 'p',
)
---
array_udiff_assoc()
array (
  'E' => 'f',
  'G' => 'I',
  'k' => 'F',
  'o' => 'p',
)
---
array_udiff_uassoc()
array (
  'G' => 'I',
  'k' => 'F',
  'o' => 'p',
)