Question

The function:

 /**
 * Retrieve post title.
 *
 * If the post is protected and the visitor is not an admin, then "Protected"
 * will be displayed before the post title. If the post is private, then
 * "Private" will be located before the post title.
 *
 * @since 0.71
 *
 * @param int $id Optional. Post ID.
 * @return string
 */

function get_the_title( $id = 0 ) {
    $post = &get_post($id);

$title = isset($post->post_title) ? $post->post_title : '';
$id = isset($post->ID) ? $post->ID : (int) $id;

if ( !is_admin() ) {
    if ( !empty($post->post_password) ) {
        $protected_title_format = apply_filters('protected_title_format', __('Protected: %s'));
        $title = sprintf($protected_title_format, $title);
    } else if ( isset($post->post_status) && 'private' == $post->post_status ) {
        $private_title_format = apply_filters('private_title_format', __('Private: %s'));
        $title = sprintf($private_title_format, $title);
    }
}
return apply_filters( 'the_title', $title, $id );
}

I don’t understand what the parameter __('Protected: %s') means in a particular line of code below. What kind of parameter is it?

$protected_title_format = apply_filters('protected_title_format', __('Protected: %s'));

Answer 1

__() is a localization function which is used to get the localized string of the English word “Protected”.

%s is a replacement parameter that is used by sprintf(). Basically, it replaces that with the title of a blog post.

The entire __('Protected: %s') call is passed as a parameter to the apply_filters() function to simply format the post title. By default I don’t think anything happens, but plugins may hook on the protected_title_format filter to further manipulate the format before applying the post title on it.