Accessing nature attributes

Hello all,
I was wondering which of these code snippets are valid ways to access 
the abstol value of a nature.

(electrical in my example is the standard electrical discipline with 
natures Voltage and Current)

module bb();
   electrical a;
   real x;
   analog begin
     x = a.potential.abstol;
     x = electrical.potential.abstol;
     x = Voltage.abstol;
   end
endmodule

I have gone through the BNF and I can't seem to find anything that 
explicitly disallows the above combinations (or maybe since it is not 
explicitly in the BNF then is is illegal). I understand that I can use 
the nature name explicitly in ddt()/idt() to access the abstol but was 
wondering if I could use hierarchical access like above.

Thanks for any help given.

Regards
Dave

-- 
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-- David Miller
-- Design Technology (Adelaide)
-- Freescale Semiconductor
-- Ph: +61-(0)8-8168 3935 Fax: x3201
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