@xdata{macmillan:name,
    publisher = {Macmillan}
}

@xdata{macmillan:place,
    location = {New York and London}
}

@xdata{macmillan,
    xdata = {macmillan:name, macmillan:place}
}

@book{key,
    author = {Author},
    title  = {Title},
    date   = {2016-11-29},
    xdata  = {macmillan}
}
