anchor.diff:  
   bsm_get_context({x,X}=Reg, #vst{current=#st{x=Xs}}=_Vst) when is_integer(X) ->
       case gb_trees:lookup(X, Xs) of
  -	{value,{match_context,_,_}=Ctx} -> Ctx;
  +	{value,#ms{}=Ctx} -> Ctx;
   	_ -> error({no_bsm_context,Reg})
       end;
   bsm_get_context(Reg, _) -> error({bad_source,Reg}).
  
positive.code: %%			Thus 'exception' is never stored as type descriptor
  %%			for a register.
  %%
  %% {match_context,_,_}	A matching context for bit syntax matching. We do allow
  %%			it to moved/to from stack, but otherwise it must only
  %%			be accessed by bit syntax matching instructions.
  %%
  
negative.code: verify_call_args({f,Lbl}, Live, Vst) when is_integer(Live)->
      Verify = fun(R) ->
  		     case get_move_term_type(R, Vst) of
  			 #ms{} ->
  			     verify_call_match_context(Lbl, Vst);
  			 _ ->
  			     ok
  