Tabs in the IDE

Kind of a dumb questions, but....

In any sketches I write, none of the #include'd modules show up in the IDE. Up until recently, I just thought that this was normal.

However, I was doing some work on the Marlin firmware for a 3D printer (a big ATMega2560 sketch) and to my surprise, all of the #include'd modules each show up as Tabs across the top of the text editor area in the IDE. It's great - I can go in and see the code. In fact, one of the #include's requires editing to set parameters for the printer.

So, how do I get the IDE to show #include's as Tabs?

Thanks.

Any files in the same folder with the sketch will show up in extra tabs. But then they are not available to other sketches. Files in the libraries folder can be included in any sketch, but don't show up in tabs with the sketch.

That makes sense. So I guess that if I want to keep a certain library version with a certain project version, I can put those files all together and any future (possibly incompatible) changes to common libraries won't effect my project. [Or won't help if the future change happens to be a fix].

Thanks.

Related question: If I want to move my functions into separate tabs, is it as simple as declaring the function heading in my main module, and then putting each function (or a few together) in a .cpp file that's saved to the same folder? Didn't seem to work when I tried it.

Also, is there a document on the IDE itself anywhere? Looked, but didn't find.

If I want to move my functions into separate tabs, is it as simple as declaring the function heading in my main module, and then putting each function (or a few together) in a .cpp file that's saved to the same folder?

Yes.

Didn't seem to work when I tried it.

Bummer.

Also, is there a document on the IDE itself anywhere?

They tried to balance one on the edge of the IDE, but it kept falling off. So, they gave up.