[sv-bc] $bits question

Is there any semantic restriction on the data type which can be passed as an
argument to $bits?

It looks to me like this argument can be syntactically a data_type, so is
this legal"

typedef bit [ $bits(enum { x }) : 0] mytype;

Where is the enumeration constant declared? In the scope containing the
declaration of "mytype"?

So is it legal to reference x outside the typedef?

mytype v;

initial

   v = mytype'(x);

 

and is the following illegal?

typedef bit [ $bits(enum { x }) : 0] mytype1;

typedef bit [ $bits(enum { x }) : 0] mytype2;  // duplicate symbol x