Cannot unset comment_notes_before

[bugnumber9]

I want to reorder comment fields by unsetting and setting them back in my chosen order. Here's my code:

function my_reorder_comments_fields( $fields ) {
	$comment_notes_before_field = $fields['comment_notes_before'];
	$comment_field = $fields['comment'];
	$author_field = $fields['author'];
	$email_field = $fields['email'];
	$url_field = $fields['url'];
	$cookies_field = $fields['cookies'];

	unset( $fields['comment_notes_before'] );
	unset( $fields['comment'] );
	unset( $fields['author'] );
	unset( $fields['email'] );
	unset( $fields['url'] );
	unset( $fields['cookies'] );

	$fields['author'] = $author_field;
	$fields['email'] = $email_field;
	$fields['comment_notes_before'] = $comment_notes_before_field;
	$fields['cookies'] = $cookies_field;
	$fields['comment'] = $comment_field;

	return $fields;
}
add_filter( 'comment_form_fields', 'my_reorder_comments_fields' );

Result - ​https://imgur.com/a/ebY1HBW
You can see that $fields['comment_notes_before'] remains on top.
To prove the point, I changed my code to just unset all fields:

function my_unset_comments_fields( $fields ) {
	unset( $fields['comment_notes_before'] );
	unset( $fields['comment'] );
	unset( $fields['author'] );
	unset( $fields['email'] );
	unset( $fields['url'] );
	unset( $fields['cookies'] );

	return $fields;
}
add_filter( 'comment_form_fields', 'my_unset_comments_fields' );

Result: ​https://imgur.com/a/B5wNngj
So $fields['comment_notes_before'] isn't getting unset while all other fields do.

[bugnumber9]

I also get a notice Undefined index: comment_notes_before that barks at $comment_notes_before_field = $fields['comment_notes_before']; in the first code.

However, it's mentioned in ​https://developer.wordpress.org/reference/functions/comment_form/, and I can access and modify it like this:

function my_change_comments_fields( $fields ) {
	$fields['comment_notes_before'] = '<p>Custom text here.</p>';
	return $fields;
}
add_filter( 'comment_form_defaults', 'my_change_comments_fields' );

[jorbin]

These filters were introduced in 3.0, so updating the version to that.

I think an automated test that demonstrates what is seen as a bug would be extremely helpful here.

[shooper]

Tested this on TwentyTwentyFour with WP 6.4.2.

I think the problem here was the wrong filter being used. The comment_notes_before is not a comment form field, but part of the comment form defaults.

Using the comment_form_defaults filter will unset that value:

function my_update_comment_defaults( $defaults ) {
    $defaults['comment_notes_before'] = '';
    return $defaults;
}
add_filter( 'comment_form_defaults', 'my_update_comment_defaults' );

[bugnumber9]

@shooper Looks like it's possible to unset all form fields (I just tested with url field) from comment_form_defaults too. Obviously, the same can be done from comment_form_fields for all fields except comment_notes_before.
Besides that, comment_notes_before is listed in ​https://developer.wordpress.org/reference/functions/comment_form/ and HTML-wise it's a part of the form - ​https://imgur.com/a/3tH6JBN