mbed-os/tools/test/config/override_with_labels/targets.json

{
    "base": {
        "extra_labels": [],
        "default_lib": "std",
        "core": "Cortex-M0"
    },
    "b1": {
        "inherits": ["base"],
        "extra_labels_add": ["b1_label"]
    },
    "b2": {
        "inherits": ["base"],
        "extra_labels_add": ["b2_label"]
    },
    "both": {
        "inherits": ["b1", "b2"]
    }
}