[sv-bc] Concat including enum as lvalue?

Once again I beg a clarification, with the usual caveat that
the answer may already be in the LRM and I've just missed it.
If that's the case, feel free to slap my wrists.

Enum variables are strongly typed in the sense that if
used as the target of an assignment, the expression
forming the right-hand side of the assignment must be
of the same enum type.  So far, so good.

Whenever an enum appears as an expression, its numeric
value may be used without explicit casting.  Also OK,
if perhaps a little free-and-easy.

So, therefore, I think the following is OK:

  enum bit[1:0] {A, B, C, D} E2;
  bit [1:0] B2;
  bit [3:0] B4;
  ...
  B4 = {B2, E2};

because E2 is silently cast to "bit [1:0]" for 
use in the expression.  But what about

  {B2, E2} = B4;

??  The tools I've tried permit this, although at least
one of them can be persuaded to generate mysteriously
wrong answers.  I can see reasonable arguments both for
and against accepting such a construct, but I don't
see the LRM pronouncing on it.

If there *is* strong type checking in such a case, then
is the following OK?

  {B2, E2} = {2'b0, E2};  // component types match

Thanks
-- 
Jonathan Bromley, Consultant

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