From Shopp Documentation

Returning Tag Results

By default, shopp() tags output results directly into your template as HTML markup. However, in some cases you may want the output of a shopp() tag returned as PHP data that can be saved in a variable for further processing, reprocessing or filtering. You can use the return option to do it. In the options parameter of any shopp() tag, simply add return=true to get the results back as data. For example, you might want to get your store's category list for processing:

<?php
$categories = shopp('catalog','category-list','return=true');
?>

A more practical example of where this comes in handy would be stripping the (0) off of categories that have no products when showing a category list that includes the number of products per category. Here's how it's done:

<?php
$categories = shopp('catalog','category-list','products=on&return=true');
$categories = str_replace('(0)','',$categories);
echo $categories;
?>

Boolean Option Values

When specifying boolean options on any shopp() tag, you can use a number of positive and negative keywords:

• true or false
• yes or no
• on or off
• 1 or 0

This can be useful for testing certain conditions using a PHP if statement.