functions-meta-box.php

<?php
add_action('add_meta_boxes_book', function () {

    add_meta_box('book-detail', '책 상세 정보', function () {
        include 'meta-box/book-detail.php';
    }, 'book');

    add_meta_box('book-cover', '책 표지', function () {
        include 'meta-box/book-cover.php';
    }, 'book');

});


add_action('edit_form_advanced', function () {

    if (get_current_screen()->post_type === 'book') {

        include 'meta-box/book-toc.php';

        include 'meta-box/book-author-intro.php';

        include 'meta-box/book-translator-intro.php';
    }

});