Override Directory for /includes Root ?

Short question. I am about to modify some files to verify correct email addresses.

What is the correct path to use for an override directory to the /includes root directory?

Specifically, the file that I am going to modify is /includes/form_check.js.

The override convention is "where ever there exists a "classic" dir, the files at that level can be overridden"

So as there is no "classic" dir at the /includes level, those files will not respect the override system and are not overrideable.

So you will have to edit the core file in this instance. I normally rename any core file that is to be altered and in your case this would be form_check.js.php to form_check.js.orig. I also include in every edited file in the commented area at the top a tag that can be grepped for later when one needs to find files altered and in my case I include the term "kobra" as it is unique. This is mainly to locate altered files quickly when and if an upgrade is to be performed.