template<typename
desc_t, typename preference_t, typename
stream_t, typename
group_t>
template<typename value_t, typename proxy_value_t = value_t>
class dx::proxy::stream::_device< desc_t, preference_t, stream_t, group_t >::chain< value_t, proxy_value_t >
drives one of the device's own promoted values through an IOCTL
Installs itself as that value's server instead of shadowing it with a second one: the device's other users - attach()'s channel buffers, info() - have to see what the driver answered, not the value the client asked for.