Why “mb_convert_encoding() expects parameter 1 to be string, array given”, if on php.net it accepts array?

$data = ['abcd', 'ddd'];
$data = mb_convert_encoding($data, 'utf-8', 'windows-1251');

I get warning: mb_convert_encoding() expects parameter 1 to be string, array given.

But according to php.net mb_convert_encoding() accepts array. See https://www.php.net/manual/en/function.mb-convert-encoding.php

mb_convert_encoding ( mixed $val , string $to_encoding [, mixed $from_encoding = mb_internal_encoding() ] ) : mixed

Converts the character encoding of val to to_encoding from optionally from_encoding. If val is an array, all its string values will be converted recursively.

Is documentation incorrect or am I stupid?

Answer

As the changelog from the documentation you mentioned describes:

7.2.0 – This function now also accepts an array as val. Formerly, only strings have been supported.

So it is going to work only for PHP in version 7.2.0 and above.