Zencart has a clever system (like many good software programs these days) of OVER-RIDES.

Basically, an OVER-RIDE system is a method of allowing you to make edits and changes to an important CORE CODE file, without changing the CORE file itself. You create a "clone" of the CORE file, edit that clone, and save it in what is commonly called the "over-rides" folder.

In zencart's case, the over-ride system is fundamentally "template based".

When you create your zencart store, one of the first things you should do is create your own CUSTOM template (essentially, your "over-ride" system).

Then, when you edit or modify a CORE CODE file, you should always save that edited file to its appropriate OVER_RIDE folder.

Some files are not part of the over-ride system, but those that are, should be treated in the appropriate way.

Start your knowledgebase here:
https://www.zen-cart.com/tutorials/i...hp?article=142