It says you should put core class extensions into application/core but this does not work. They only work when you put them into application/libraries. I was not sure if the documentation or the loader should be updated for this but it made more sense to have the documentation match first and then the loader AND documentation change later if necessary.
Which version of CI are are you using?
And which class are you trying to extend or replace?
2.1.2, and it was both the Form_validation and Security classes. Neither were even being looked at, as I intentionally broke the syntax of the files to cause an error, but no errors occurred until the files were moved into application/libraries. I'm content to leave them there for now, but as it stands either the documentation or the core is not up-to-date.
I have not messed with core at all.
The only files supposed to go in application/core are to overwrite files in system/core
application/libraries overwrites system/libraries.
This is the correct behavior.
That makes sense.
However, not in the context of the documentation. Since everyone refers to the system folder as "core", it would only make sense that everything falls under that moniker. The documentation sounds like it needs a note to distinguish between core core classes and core libraries and how extending them differs.
The issue I have with it is that It's not immediately obvious, and I've been using CI for a couple years now. I should probably have known the difference, but I had never needed to extend any of the core libraries until recently.