Can we have files without or with made-up extensions?

Question

Is it possible to save, say, a C++ program without the .cpp and still be recognized by a compiler, or an HTML document without the .html or .xhtml and still be opened by a web browser?
I have seen files without extensions and with extensions like .common and .old but no other type of extension following it, and it still works, so I guess I partly answered this, but could it always work?

Answer 1

You can create your own extensions if you want. However, if you're changing the extensions that a compilers recognizes, then you'll need to also change the compiler/makefile itself to recognize your new extensions. Likewise, your OS and other applications use extensions to know what the file is and what it's used for, so just be cautious of that as well.

Browsers and the internet are a bit different than your local stuff. What's your objective with it? There is usually a workaround for whatever our goal is.