How to use wp_category_checklist()?

Question

I've recently discovered that we can insert a dropdown list of categories like this:

<?php
define( 'WP_USE_THEMES', false );
require( './wp-load.php' );
?>
<?php wp_dropdown_categories(array(
                            'child_of' => 0,
                            'class' => 'postform', 
                            'depth' => 0,
                            'echo' => 1,
                            'exclude' => '', 
                            'hide_empty' => false, 
                            'hide_if_empty' => false,
                            'hierarchical' => true,
                            'id' => '',
                            'name' => 'cat-dropdown', 
                            'order' => 'ASC',
                            'orderby' => 'name', 
                            'selected' => 0, 
                            'show_count' => 0,
                            'show_option_all' => '', 
                            'show_option_none' => __('None'),
                            'tab_index' => 0, 
                            'taxonomy' => 'format',
                        )); ?>

Which is great. BUT, what if I want to select multiple categories?

I've come across wp_category_checklist() and tried this code:

<?php function wp_category_checklist( $post_id = 0, $descendants_and_self = 0, $selected_cats = false, $popular_cats = false, $walker = null, $checked_ontop = true ) {
wp_terms_checklist( $post_id, array(
    'taxonomy' => 'category',
    'descendants_and_self' => $descendants_and_self,
    'selected_cats' => $selected_cats,
    'popular_cats' => $popular_cats,
    'walker' => $walker,
    'checked_ontop' => $checked_ontop
) );
} ?>

But it doesn't output anything.

I'm trying to get a list of my categories on a BLANK PAGE, not within a sidebar or post.

Is what I want possible?

Answer 1

Here is the answer:

$select_cats = wp_dropdown_categories( array( 'echo' => 0 ) );
$select_cats = str_replace( "name='cat' id=", "name='cat[]' multiple='multiple' id=", $select_cats );
echo $select_cats;