// one more overload before ...
template< typename Selector, typename Head, typename Tail,
    typename Default, typename ToSelect, typename Selected >
auto runIfValid( Selector &sel, Head, Tail, Default,
        ToSelect, Selected, Preferred, NotPreferred )
    -> typename std::enable_if<
        ! std::is_base_of< InstantiationError, Head >::value
        && EvalBoolExpr< ContainsP< Selected >::template Elem,
            typename Head::SupportedBy >::value,
        typename Selector::ReturnType >::type
{
    return sel.ifSelect( Head(), [ &sel ]() {
            return runSelector( sel, ToSelect(),
                typename Append< Head, Selected >::T() );
        }, [ &sel ]() {
            return runOne( sel, Tail(), Default(),
                ToSelect(), Selected() );
        } );
} // and one after ...