Re: rvalue reference questions

I was reading about rvalue refernces in this link
http://www.artima.com/cppsource/rvalue.html

Most of the thing seems clear to me. But I'm confused in certain
parts

For eg:
In the section Overloading on lvalue / rvalue

<quote>

class Derived
   : public Base
{
   std::vector<int> vec;
   std::string name;
   // ...
public:
   // ...
   // move semantics
   Derived(Derived&& x) // rvalues bind here
       : Base(std::move(x)),
         vec(std::move(x.vec)),
         name(std::move(x.name)) { }

   Derived& operator=(Derived&& x) // rvalues bind here
   {
       Base::operator=(std::move(x));
       vec = std::move(x.vec);
       name = std::move(x.name);
       return *this;
   }
   // ...
};

Note above that the argument x is treated as an lvalue internal to
the move functions, even though it is declared as an rvalue
reference parameter. That's why it is necessary to say move(x)
instead of just x when passing down to the base class. This is a
key safety feature of move semantics designed to prevent
accidentally moving twice from some named variable. All moves occur
only from rvalues, or with an explicit cast to rvalue such as using
std::move. If you have a name for the variable, it is an lvalue.
</Quote>

In this case how the compiler convert the rvalue reference parameter
as lvalue?

And when the question of double-moving comes? Can someone give an
example.