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

{
    "base": {
        "supported_toolchains": ["GCC_ARM"],
        "extra_labels": [],
        "default_lib": "std",
        "core": "Cortex-M0",
        "config": {
            "par1": "v_par1_base",
            "par2": "v_par2_base",
            "par3": "v_par3_base"
        }
    },
    "b1": {
        "inherits": ["base"],
        "extra_labels_add": ["b1_label"],
        "overrides": {
            "par1": "v_par1_b1"
        }
    },
    "b2": {
        "inherits": ["base"],
        "extra_labels_add": ["b2_label"],
        "overrides": {
            "par2": "v_par2_b2"
        }
    },
    "both": {
        "inherits": ["b1", "b2"],
        "config": {
            "par4": "v_par4_both"
        },
        "overrides": {
            "par3": "v_par3_both"
        }
    }
}