mmengine/tests/data/config/json_config/test_base.json

{
    "_base_": [
        "../py_config/base1.py",
        "../yaml_config/base2.yaml",
        "./base3.json",
        "../py_config/base4.py"
    ],
    "item3": false,
    "item4": "test",
    "item8": "{{fileBasename}}",
    "item9": {{ _base_.item2 }},
    "item10": {{ _base_.item7.b.c }}
}