[sv-ec] Derived classes and package imports

This is probably a really stupid question, but it has
me a little confused.

Suppose I have a base class declared in a package:

  package P;
    class B;
      logic L;
    endclass : B
  endpackage : P

and then I want an extension of B but I don't want
to modify the original package's source code.  
So I write a new package:

  package Q;
    import P::*;  // to get definition of B
    class C extends B;
      logic M;
    endclass : C
  endpackage : Q

So far, so good; but now I try to use this:

  program PP;
    import Q::*;  // gets C, but no chained import of P
    C c = new;  // OK
    initial begin
      $display(c.M);  // definitely OK
      $display(c.L);  // is this OK?  I guess so.
    end
    initial begin
      B b;  // can I do this?  I guess not.
      b = c;  // typical upcast
    end
  endprogram : PP

In other words: If I import a package containing a definition
of a class derived from a class it imports from another package,
how much of the base class definition can I see?

Usual apologies in advance if this is something obvious I
should have known already.
-- 
Jonathan Bromley, Consultant

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