WordPress at a glance
filter is not described

comment_notification_subject filter-hook . WP 1.5.2

Filters the comment notification email subject.

Usage

add_filter( 'comment_notification_subject', 'filter_function_name_9555', 10, 2 );
function filter_function_name_9555( $subject, $comment_id ){
	// filter...

	return $subject;
}
$subject(string)
The comment notification email subject.
$comment_id(int)
Comment ID.

Where the hook is called

wp_notify_postauthor()
wp-includes/pluggable.php 1558
$subject = apply_filters( 'comment_notification_subject', $subject, $comment->comment_ID );

Where the hook is used (in WP core)

Does not used.