anchor.diff:  
   usertype_variable_declaration   : (Automatic)? user_type (dimension)? list_of_variable_descriptions ;
   
  -string_declaration  :   String list_of_variable_descriptions ;
  +string_declaration  :   SVString list_of_variable_descriptions ;
   
   struct_declaration  :   struct_type list_of_variable_descriptions ;
   
  
positive.code:                 | Realtime
                  | Time
                  | Reg
                  | String
                  | bits_type
                  | user_type
                  ;
  
negative.code:                 //| Realtime
                  //| Time
                  //| Reg
                  //| SVString
                  //| bits_type
                  ;
  
  