In a site where I have 2 similar forms in different pages, since some of the fields are the same, it seems logical I should have one class that validates the fields from both forms.
My question is, where should such a class reside? In /assets? In /includes?
This question goes for any other files (such as 3rd party scripts) as well.
What is the best organization practice for files that do not fall in the /controller and /model directories?
“Assets” generally refers to static assets like images and CSS files, so that’s out. If you’re not using an MVC framework or if the framework you’re using that doesn’t have a convention for this (try googling around) I’d recommend creating a directory like
/lib,/lib/validators, or perhaps/common. In the end it’s most important to pick something that makes sense to you (and other developers who might be working on the project). You can always move files around later if you realize a different structure might be better.