[sv-ec] Upward referencing rules question

I cannot find rules for below reference in SV.I'm using reference to a1.num
in named block "oo". In this block there is object variable named a1 but it
has no "num" funcion 
The question is: Should seraching for matching function be stopped at this
level or should the search be continued into module scope - where is "a1"
instance which have "num" function.
So below case should return error, or it should compile and return "5" in
simulation?
 
 
module M;
 function integer num();
  num= 5;
 endfunction
endmodule
 
class C;
        reg r;
endclass
 
module top;
 M a1();
 
 initial begin : oo
 C a1;
 $display(a1.num());
 end
endmodule

 
DANiel

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