Page source:

// azn is of  Page Type 'URL', so extract the URL returned by calling it
var dispatch = WubCall(funcname, [arg]);
var u = (WubCall("siteutil.GetURLFromURLFunction", [dispatch]) ? nil);

var res = false;
if u != nil then
   var P = (GetURL(u) ? nil);
   if (P != nil) then
      var T = Pat(P, testStr); // Look for the test string
      res = (Size(T) > 0);
   end;
end;
res;