Making a dictionary inside a list, or, what’s really happening inside R lists?

{
    "id": "label",
    "name": "title for set",
    "contents": [
        {
            "id": "A",
            "hash": 1234
        },
        {
            "id": "B",
            "hash": 5678
        },
        {
            "id": "C",
            "hash": 7890,
            "sub_contents": {
                "1": 12345
                "2": 67890
                "3": 11234
            }
         }
    ]
}