Zen Cart extensibility
From Wiki @ Karl Jones dot com
Zen Cart extensibility is the extensibility principle as it applies to Zen Cart.
Plugins
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Observer class
The Observer Class allows a plugin to listen for for (observe) an event (a notification) and provide additional processing.
This notifier/observer interface also works in the Zen Cart admin panel.
Adding a notifier at specific processing points in the popular (e.g. orders.php, customer.php) admin pages, and providing observer code to insert their customization, may help installation and upgrade processes go much more smoothly.
