vars: {
    Apple: {
        shape:circle
        label:Granny Smith
    }
    Cherry: {
        shape:circle
        label:Rainier Cherry
    }
    SummerFruit: {
        xx: ${Apple}   # Could not resolve
        cc: ${Cherry}  # Could not resolve
        xx -> cc
    }
}

x: ${Apple}   # ok
c: ${Cherry}  # ok
x -> c
sf: ${SummerFruit} # doesn't get this far
```d2