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

{
    "base": {
        "supported_toolchains": ["GCC_ARM"],
        "extra_labels": [],
        "default_lib": "std",
        "core": "Cortex-M0"
    },
    "left_intermediate": {
        "inherits": ["base"],
        "extra_labels_add": ["left_intermediate_label"]
    },
    "right_intermediate": {
        "inherits": ["base"],
        "extra_labels_add": ["right_intermediate_label"]
    },
    "both": {
        "inherits": ["left_intermediate", "right_intermediate"]
    }
}