问帮助理解WordPress下拉列表代码

EN

<?php if ( is_taxonomy_hierarchical($taxonomy) ) : ?>
    <tr class="form-field term-parent-wrap">
        <th scope="row"><label for="parent"><?php _ex( 'Parent', 'term parent' ); ?></label></th>
        <td>
            <?php
            $dropdown_args = array(
                'hide_empty'       => 0,
                'hide_if_empty'    => false,
                'taxonomy'         => $taxonomy,
                'name'             => 'parent',
                'orderby'          => 'name',
                'selected'         => $tag->parent,
                'exclude_tree'     => $tag->term_id,
                'hierarchical'     => true,
                'show_option_none' => __( 'None' ),
            );

            /** This filter is documented in wp-admin/edit-tags.php */
            $dropdown_args = apply_filters( 'taxonomy_parent_dropdown_args', $dropdown_args, $taxonomy, 'edit' );
            wp_dropdown_categories( $dropdown_args ); ?>
            <?php if ( 'category' == $taxonomy ) : ?>
            <p class="description"><?php _e('Categories, unlike tags, can have a hierarchy. You might have a Jazz category, and under that have children categories for Bebop and Big Band. Totally optional.'); ?></p>
            <?php endif; ?>
        </td>
    </tr>