Keeping the 'node' as an object even though it has children and is not a leaf

If one has following structure producing /foo object

$ tree
.
└── foo
    └── main.fmf

adding another fmf file makes the original node stop being leaf and thus disapearing from the fmf tree

$ tree
.
└── foo
    ├── bar.fmf
    └── main.fmf
$ fmf ls
/foo/bar

Proposal to add marker similar to /: inherit:false which would keep the /foo being an object, thus for the above tree we will have:

$ fmf ls
/foo
/foo/bar

Name of the marker subject to discussion: how about retain-name?

Related tmt issue: tmt/issues/1795

teemtee / fmf