There may be a collision between Virtual Boy ROM files and Visual Basic source files.

(In reply to Adrien Plazas from comment #1)
> There may be a collision between Virtual Boy ROM files and Visual Basic
> source files.

Which could be a reason for it to need magic.

(In reply to Bastien Nocera from comment #2)
> Which could be a reason for it to need magic.

Unfortunately I didn't find interesting information about that, IIUC the header is at the end of the file, it doesn't contain useful information in our case, and I couldn't verify this information on the files I found… hence the absence of a magic in my patch.

I'll keep exploring.

(In reply to Adrien Plazas from comment #3)
> I'll keep exploring.

I confirm that there is no header but a footer, and I didn't see any magic value in it.

Could there be one in Visual Basic source code files?

commit 802530ada012a36ed63c4c15e7547b88582e7b79
Author: Adrien Plazas <kekun.plazas@laposte.net>
Date:   Sun May 21 13:18:31 2017 +0200

    Add application/x-virtual-boy-rom
    
    There may be a collision between Virtual Boy ROM files and Visual
    Basic source files, but those don't have any test files, so we
    cannot know.
    
    https://bugs.freedesktop.org/show_bug.cgi?id=101137