Yes, which comes out quite nicely in situations like ImplicitlyConvertibleTo, in your NamedType library, written as:

template <typename T>
struct ImplicitlyConvertibleTo {
template <typename C>
struct skill {
// code for implicit conversion of C to T
};
};

using MyType = NamedType<int, struct MyTypeTag, ImplicitlyConvertibleTo<double>>;

Ok then if I understand well all skills (simple or composite) are implemented as nested classes? Thanks for sharing!

The technique I used in my experimental strong_type lib is (changed names to match your blog post, and maybe introduced some errors) as follows:

template <typename S, typename T>
using skill = typename S::template skill<T>;

template <typename … S>
class C : public skill<S, C<S…>>…
{
…
};

A skill is then implemented in its sub template type named skill.

struct Feature1 {
template <typename T>
struct skill {
static_cast<T*>(this)->foo();
};
};