How do I make use of the AssetImporter class to import custom asset formats?

I need to import a custom asset format in to Unity using the AssetImporter class. The documentation is rather sparse on its usage and I have reached an impasse in the development. Has anyone actually used AssetImporter to create their own asset import class? I have scoured every resource looking for a suitable answer but it appears that nobody is using this particular feature of the framework.

As far as I know Unity doesn’t support that properly.

Although there is a nice workaround: implement AssetPostprocessor.OnPostprocessAllAssets (Unity - Scripting API: AssetPostprocessor.OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths, bool didDomainReload)), there you can create prefabs (or whatever) based on imported files with your custom file formats.