Plugin API
From Shopp Documentation
Actions and Filters
Shopp is not only built on top of the WordPress API, but it re-implements it to allow other WordPress plugins to interact and extend Shopp's capabilities. This is done primarily through WordPress action and filter hooks.
For more information about getting started using WordPress action/filter hooks, see the WordPress Codex Plugin API article. Below are links to reference articles about Shopp's implementation of action hooks and filter hooks you can use in your own plugins and theme functions.
Template API Usage
Shopp's Template API is not only for the theme templates. You can also use portions of Template API to load information contexts (such as Categories, Products, Purchases, etc.), and obtain information about those objects in a way that will remain consistent from one Shopp version to the next.
Directly accessing Shopp data structures if possible, but lacks the "future proofing" benefits of using the Template API whenever possible.
