Placeholder in HTML editor text area?

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Solved it:

function add_placeholder_event( $html ){
$screen = get_current_screen();
$post_type = $screen->post_type;

if( $post_type == 'event' ) {
    $html = preg_replace('/<textarea/', '<textarea placeholder="John Doe" ', $html);
}
return $html;
}
add_filter('the_editor','add_placeholder_event');