What are the best practices for organizing and managing child categories within a PHP metabox?

When organizing and managing child categories within a PHP metabox, it is important to properly structure the data and ensure that child categories are displayed in a hierarchical manner. One way to achieve this is by using the `wp_dropdown_categories` function with the `hierarchical` parameter set to true. This will display the categories in a nested dropdown format, making it easier for users to select the appropriate child category. 

// Display hierarchical dropdown of categories in a metabox
function custom_category_metabox() {
    ?>
    <select name="category_id" id="category_id">
        <option value="">Select Category</option>
        <?php
        $args = array(
            'taxonomy' => 'category',
            'show_option_all' => '',
            'hierarchical' => true
        );
        wp_dropdown_categories($args);
        ?>
    </select>
    <?php
}

// Save selected category
function save_custom_category_metabox($post_id) {
    if (isset($_POST['category_id'])) {
        wp_set_post_categories($post_id, array($_POST['category_id']));
    }
}
add_action('save_post', 'save_custom_category_metabox');

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