1. Navigate to the ch4-book-reviews folder of the WordPress plugin directory of your development installation.
2. Open the ch4-book-reviews.php file in a code editor.
3. Add the following line of code after the existing functions to register a function to be called when the administration interface is visited:

add_action( 'admin_init', 'ch4_br_admin_init' ); 

4. Add the following code section to provide an implementation for the ch4_br_admin_init function and register a meta box to be associated with the book_reviews post type:

function ch4_br_admin_init() { 
    add_meta_box( 'ch4_br_review_details_meta_box',  
                  'Book Review Details', 
                  'ch4_br_display_review_details_meta_box', 
                  'book_reviews', 'normal', 'high' ); 
} 

5. Insert this function to implement the ch4_br_display_review_details_meta_box function and render the meta box contents:

function ch4_br_display_review_details_meta_box( $book_review ) {  
    // Retrieve current author and rating based on review ID 
    $book_author = 
          esc_html( get_post_meta( $book_review->ID, 
                                   'book_author', true ) ); 
    $book_rating = 
          intval( get_post_meta( $book_review->ID,
                                 'book_rating', true ) ); 
    ?> 
    <table> 
        <tr> 
            <td style="width: 100%">Book Author</td> 
            <td><input type="text" size="80" 
                       name="book_review_author_name" 
                       value="<?php echo $book_author; ?>" /></td> 
        </tr> 
        <tr> 
            <td style="width: 150px">Book Rating</td> 
            <td> 
                <select style="width: 100px" 
                        name="book_review_rating"> 
                <!-- Loop to generate items in dropdown list -->
                <?php
                for ( $rating = 5; $rating >= 1; $rating -- ) { ?> 
                <option value="<?php echo $rating; ?>"
                <?php echo selected( $rating, $book_rating ); ?>>
                <?php echo $rating; ?> stars 
                <?php } ?> 
                </select> 
            </td> 
        </tr> 
    </table> 
 <?php } 

6. Add the following code segment to register a function that will be called when posts are saved to the database:

add_action( 'save_post', 'ch4_br_add_book_review_fields', 10, 2 ); 

7. Add an implementation for the ch4_br_add_book_review_fields function defined in the previous add_action call:

function ch4_br_add_book_review_fields( $book_review_id,
                                        $book_review ) { 
    // Check post type for book reviews 
    if ( 'book_reviews' == $book_review->post_type ) { 
        // Store data in post meta table if present in post data 
        if ( isset( $_POST['book_review_author_name'] ) ) {
            update_post_meta( $book_review_id, 'book_author', 
                sanitize_text_field( 
                    $_POST['book_review_author_name'] ) ); 
        } 
         
        if ( isset( $_POST['book_review_rating'] ) && 
             !empty( $_POST['book_review_rating'] ) ) {            
            update_post_meta( $book_review_id, 'book_rating', 
                intval( $_POST['book_review_rating'] ) ); 
        } 
    } 
} 

8. Find the ch4_br_create_book_post_type function, where the new book type was originally created, and remove the custom-fields element from the supports array:

   'supports' => array( 'title', 'editor', 'comments', 'thumbnail' ), 

9. Save and close the plugin file.
10. Open the previously created Book Review to see the new Book Review Details meta box, containing a text field to specify the author and a drop-down list for the rating: