How to make QML applications with multiple files using the same technique as is done with Qt and Widgets?

Unlike in C/C++ you don’t need to include or import other QML files that are part of your project. You just need to add the extra QML files and you can directly use them as components, since each QML file can only have one root component. This is not the case with JS files, you still have to import them. Also the same goes for custom C++ components.