Can't register FileEditorProvider that handles directories?

So I want to handle directories with extension `.mllt`. I already registered a `FileTypeFactory`, and now I'm trying to use a `FileEditorProvider`. I monitored the invocation `accept` calls, and it appears that IntelliJ simply ignores directories. That is, I can see `accept` calls when double clicking on an unknown file, but my example, `workspace.mllt`, is simply shown as a tree branch and double clicking in the project view shows the internals of that directory instead of attempting to find an editor.

Is there a way to solve this? You can imagine `workspace.mllt` to be something like a jar file, only that technically it is a directory.

So this is how it looks, and I have a crappy workaround by associating the editor with a dummy file called 'open':

and this is how it should be:

Thanks, ..h.h..