anchor.diff:     : [a-zA-Z_] [a-zA-Z0-9_$]*
      ;
   
  -
   Dollar_Identifier
      : '$' [a-zA-Z0-9_$] [a-zA-Z0-9_$]*
      ;
   
   
   Time_Identifier
  -   : [0-9] + [mnpf] 's'
  +   : [0-9] + [mnpf]? 's'
      ;
   
   system_function_identifier
  
positive.code: 
  // 2.2.2 Strengths
  drive_strength
     : (strength0 ',' strength1)
     | (strength1 ',' strength0)
     | (strength0 ',' 'highz1')
     | (strength1 ',' 'highz0')
     | ('highz0' ',' strength1)
     | ('highz1' ',' strength0)
     ;
  
  strength0
  
negative.code:    | attribute_instance* parameter_override
     | attribute_instance* continuous_assign
     | attribute_instance* gate_instantiation
  //   | attribute_instance* udp_instantiation
     | attribute_instance* module_instantiation
     | attribute_instance* initial_construct
     | attribute_instance* always_construct
  