In trying to add support for Clang module maps to Qt i ended up in maze of unclear and inconsistent definitions when it comes to what a "module" is in Qt these days, and whether these are "private", "public", "implementation", "internal", etc.

• How can I distinguish a Qt module in the traditional sense, ie one with public C++ headers, e.g. QtGui, from all the other "modules" we generate as part of a build these days?
• Why is ExamplesAssetDownloaderPrivate a private `INTERNAL_MODULE`, but QmlAssetDownloader is not?
• Why do we have both QuickControls2FusionStyle and QuickControls2FusionStyleImpl, if none of them include public C++ headers?
  • Why are neither of these marked as private/internal/something?
    • They are an implementation detail of the QML API, no?

Can someone who has the full picture explain all of this?